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In their analysis of data from the National Weight Control Registry, Klem and coworkers found that weight loss achieved through exercise, sensible dieting, reduced fat consumption, and individual behavior changes could be maintained for long periods of time. However, this population was self-selected so it does not represent the experience of the average person in a civilian population.

Because they have achieved and maintained a significant amount of weight loss at least 30 lb for 2 or more years , there is reason to believe that the population enrolled in the Registry may be especially disciplined. As such, the experience of people in the Registry may provide insight into the military population, although evidence to assert this with authority is lacking. In any case, the majority of participants in the Registry report they have made significant permanent changes in their behavior, including portion control, low-fat food selection, 60 or more minutes of daily exercise, self-monitoring, and well-honed problem-solving skills.

A significant part of weight loss and management may involve restructuring the environment that promotes overeating and underactivity. The environment includes the home, the workplace, and the community e. Environmental factors include the availability of foods such as fruits, vegetables, nonfat dairy products, and other foods of low energy density and high nutritional value.

Environmental restructuring empha-sizes frequenting dining facilities that produce appealing foods of lower energy density and providing ample time for eating a wholesome meal rather than grabbing a candy bar or bag of chips and a soda from a vending machine. Busy lifestyles and hectic work schedules create eating habits that may contribute to a less than desirable eating environment, but simple changes can help to counter-act these habits. Commanders of military bases should examine their facilities to identify and eliminate conditions that encourage one or more of the eating habits that promote overweight.

Some nonmilitary employers have increased healthy eating options at worksite dining facilities and vending machines. Although multiple publications suggest that worksite weight-loss programs are not very effective in reducing body weight Cohen et al. Opting for high-fat snack foods from strategically placed vending machines or snack shops combined with allowing insufficient time to prepare affordable, healthier alternatives. Major obstacles to exercise, even in highly motivated people, include the time it takes to complete the task and the inaccessibility of facilities or safe places to exercise.

Environmental interventions emphasize the many ways that physical activity can be fit into a busy lifestyle and seek to make use of whatever opportunities are available HHS, The availability of safe sidewalks and parks and alternative methods of transportation to work, such as walking or bicycling, also enhance the physical activity environment. Management of overweight and obesity requires the active participation of the individual.

Nutrition professionals can provide individuals with a base of information that allows them to make knowledgeable food choices. Nutrition education is distinct from nutrition counseling, although the contents overlap considerably. Nutrition counseling and dietary management tend to focus more directly on the motivational, emotional, and psychological issues associated with the current task of weight loss and weight management. It addresses the how of behavioral changes in the dietary arena. Nutrition education on the other hand, provides basic information about the scientific foundation of nutrition that enables people to make informed decisions about food, cooking methods, eating out, and estimating portion sizes.

Nutrition education programs also may provide information on the role of nutrition in health promotion and disease prevention, sports nutrition, and nutrition for pregnant and lactating women. Effective nutrition education imparts nutrition knowledge and its use in healthy living.

For example, it explains the concept of energy balance in weight management in an accessible, practical way that has meaning to the individual's lifestyle, including that in the military setting.

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Written materials prepared by various government agencies or by nonprofit health organizations can be used effectively to provide nutrition education. However, written materials are most effective when used to reinforce informal classroom or counseling sessions and to provide specific information, such as a table of the calorie content of foods. The format of education programs varies considerably, and can include formal classes, informal group meetings, or teleconferencing.

A common background among group members is helpful but seldom possible. Educational formats that provide practical and relevant nutrition information for program participants are the most successful. For example, some military weight-management programs include field trips to post exchanges, restaurants fast-food and others , movies, and other places where food is purchased or consumed Vorachek, The involvement of spouses and other family members in an education program increases the likelihood that other members of the household will make permanent changes, which in turn enhances the likelihood that the program participants will continue to lose weight or maintain weight loss Hart et al.

Particular attention must be directed to involvement of those in the household who are most likely to shop for and prepare food. Unless the program participant lives alone, nutrition management is rarely effective without the involvement of family members. Weight-management programs may be divided into two phases: While exercise may be the most important element of a weight-maintenance program, it is clear that dietary restriction is the critical component of a weight-loss program that influences the rate of weight loss.

Activity accounts for only about 15 to 30 percent of daily energy expenditure, but food intake accounts for percent of energy intake. Thus, the energy balance equation may be affected most significantly by reducing energy intake.

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The number of diets that have been proposed is almost innumerable, but whatever the name, all diets consist of reductions of some proportions of protein, carbohydrate CHO and fat. The following sections examine a number of arrangements of the proportions of these three energy-containing macronutrients. A nutritionally balanced, hypocaloric diet has been the recommendation of most dietitians who are counseling patients who wish to lose weight.

This type of diet is composed of the types of foods a patient usually eats, but in lower quantities. There are a number of reasons such diets are appealing, but the main reason is that the recommendation is simple—individuals need only to follow the U. Department of Agriculture's Food Guide Pyramid. The Pyramid recommends that individuals eat a variety of foods, with the majority being grain products e. In using the Pyramid, however, it is important to emphasize the portion sizes used to establish the recommended number of servings.

For example, a majority of consumers do not realize that a portion of bread is a single slice or that a portion of meat is only 3 oz. A diet based on the Pyramid is easily adapted from the foods served in group settings, including military bases, since all that is required is to eat smaller portions. Even with smaller portions, it is not difficult to obtain adequate quantities of the other essential nutrients.

Many of the studies published in the medical literature are based on a balanced hypocaloric diet with a reduction of energy intake by to 1, kcal from the patient's usual caloric intake. Meal replacement programs are commercially available to consumers for a reasonably low cost. The meal replacement industry suggests replacing one or two of the three daily meals with their products, while the third meal should be sensibly balanced.

In addition, two snacks consisting of fruits, vegetables, or diet snack bars are recommended each day. A number of studies have evaluated long-term weight maintenance using meal replacement, either self-managed Flechtner-Mors et al. The largest amount of weight loss occurred early in the studies about the first 3 months of the plan Ditschuneit et al.

One study found that women lost more weight between the third and sixth months of the plan, but men lost most of their weight by the third month Heber et al. All of the studies resulted in maintenance of significant weight loss after 2 to 5 years of follow-up. Hill's review of Rothacker pointed out that the group receiving meal replacements maintained a small, yet significant, weight loss over the 5-year program, whereas the control group gained a significant amount of weight.

Active intervention, which included dietary counseling and behavior modification, was more effective in weight maintenance when meal replacements were part of the diet Ashley et al. Meal replacements were also found to improve food patterns, including nutrient distribution, intake of micronutrients, and maintenance of fruit and vegetable intake.

Long-term maintenance of weight loss with meal replacements improves biomarkers of disease risk, including improvements in levels of blood glucose Ditschuneit and Fletchner-Mors, , insulin, and triacylglycerol; improved systolic blood pressure Ditschuneit and Fletchner-Mors, ; Ditschuneit et al. Winick and coworkers evaluated employees in high-stress jobs e. The meal replacements were found to be effective in reducing weight and maintaining weight loss at a 1-year follow-up.

In contrast, Bendixen and coworkers reported from Denmark that meal replacements were associated with negative outcomes on weight loss and weight maintenance. However, this was not an intervention study; participants were followed for 6 years by phone interview and data were self-reported. Unbalanced, hypocaloric diets restrict one or more of the calorie-containing macronutrients protein, fat, and CHO. The rationale given for these diets by their advocates is that the restriction of one particular macronutrient facilitates weight loss, while restriction of the others does not.

Many of these diets are published in books aimed at the lay public and are often not written by health professionals and often are not based on sound scientific nutrition principles. For some of the dietary regimens of this type, there are few or no research publications and virtually none have been studied long term.

Therefore, few conclusions can be drawn about the safety, and even about the efficacy, of such diets. The major types of unbalanced, hypocaloric diets are discussed below. There has been considerable debate on the optimal ratio of macronutrient intake for adults. This research usually compares the amount of fat and CHO; however, there has been increasing interest in the role of protein in the diet Hu et al. Although the high-protein diet does not produce significantly different weight loss compared with the high-CHO diet Layman et al.

High-protein, low-CHO diets were introduced to the American public during the s and s by Stillman and Baker and by Atkins Atkins, ; Atkins and Linde, , and more recently, by Sears and Lawren While most of these diets have been promoted by nonscientists who have done little or no serious scientific research, some of the regimens have been subjected to rigorous studies Skov et al.

There remains, however, a lack of randomized clinical trials of 2 or more years' duration, which are needed to evaluate the potent beneficial effect of weight loss accomplished using virtually any dietary regimen, no matter how unbalanced on blood lipids. In addition, longer studies are needed to separate the beneficial effects of weight loss from the long-term effects of consuming an unbalanced diet. These claims are unsupported by scientific data.

Although these diets are prescribed to be eaten ad libitum, total daily energy intake tends to be reduced as a result of the monotony of the food choices, other prescripts of the diet, and an increased satiety effect of protein. Thus, the relatively rapid initial weight loss that occurs on these diets predominantly reflects the loss of body water rather than stored fat.

This can be a significant concern for military personnel, where even mild dehydration can have detrimental effects on physical and cognitive performance. For example, small changes in hydration status can affect a military pilot's ability to sense changes in equilibrium. Results of several recent studies suggest that high-protein, low-CHO diets may have their benefits. In addition to sparing fat-free mass Piatti et al. Furthermore, a percent protein diet reduced resting energy expenditure to a significantly lesser extent than did a percent protein diet Baba et al.

The length of these studies that examined high-protein diets only lasted 1 year or less; the long-term safety of these diets is not known. Low-fat diets have been one of the most commonly used treatments for obesity for many years Astrup, ; Astrup et al. The most extreme forms of these diets, such as those proposed by Ornish and Pritikin , recommend fat intakes of no more than 10 percent of total caloric intake.

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Although these stringent diets can lead to weight loss, the limited array of food choices make them difficult to maintain for extended periods of time by individuals who wish to follow a normal lifestyle. More modest reductions in fat intake, which make a dietary regimen easier to follow and more acceptable to many individuals, can also promote weight loss Astrup, ; Astrup et al. For example, Sheppard and colleagues reported that after 1 year, obese women who reduced their fat intake from approximately 39 percent to 22 percent of total caloric intake lost 3.

Results of recent studies suggest that fat restriction is also valuable for weight maintenance in those who have lost weight Flatt ; Miller and Lindeman, Dietary fat reduction can be achieved by counting and limiting the number of grams or calories consumed as fat, by limiting the intake of certain foods for example, fattier cuts of meat , and by substituting reduced-fat or nonfat versions of foods for their higher fat counterparts e. Over the past decade, pursuit of this latter strategy has been simplified by the burgeoning availability of low-fat or fat-free products, which have been marketed in response to evidence that decreasing fat intake can aid in weight control.

The mechanisms for weight loss on a low-fat diet are not clear. Weight loss may be solely the result of a reduction in total energy intake, but another possibility is that a low-fat diet may alter metabolism Astrup, ; Astrup et al. Support for the latter possibility has come from studies showing that the short-term adherence to a diet containing 20 or 30 percent of calories from fat increased hour energy expenditure in formerly obese women, relative to an isocaloric diet with 40 percent of calories from fat Astrup et al.

Over the past two decades, fat consumption as a percent of total caloric intake has declined in the United States Anand and Basiotis, , while average body weight and the proportion of the American population suffering from obesity have increased significantly Mokdad et al. Several factors may contribute to this seeming contradiction. First, all individuals appear to selectively underestimate their intake of dietary fat and to decrease normal fat intake when asked to record it Goris et al. If these results reflect the general tendencies of individuals completing dietary surveys, then the amount of fat being consumed by obese and, possibly, nonobese people, is greater than routinely reported.

Second, although the proportion of total calories consumed as fat has decreased over the past 20 years, grams of fat intake per day have remained steady or increased Anand and Basiotis, , indicating that total energy intake increased at a faster rate than did fat intake. Coupled with these findings is the fact that since the early s, the availability of low-fat and nonfat, but calorie-rich snack foods e.

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However, total energy intake still matters, and overconsumption of these low-fat snacks could as easily lead to weight gain as intake of their high-fat counterparts Allred, Two recent, comprehensive reviews have reported on the overall impact of low-fat diets. Astrup and coworkers examined four meta-analyses of weight change that occurred on intervention trials with ad libitum low-fat diets. They found that low-fat diets consistently demonstrated significant weight loss, both in normal-weight and overweight individuals.

A dose-response relationship was also observed in that a 10 percent reduction in dietary fat was predicted to produce a 4- to 5-kg weight loss in an individual with a BMI of Most low-fat diets are also high in dietary fiber, and some investigators attribute the beneficial effects of low-fat diets to the high content of vegetables and fruits that contain large amounts of dietary fiber.

The rationale for using high-fiber diets is that they may reduce energy intake and may alter metabolism Raben et al. The beneficial effects of dietary fiber might be accomplished by the following mechanisms: Dietary fiber is not a panacea, and the vast majority of controlled studies of the effects of dietary fiber on weight loss show minimal or no reduction in body weight LSRO, ; Pasman et al. Many individuals and companies promote the use of dietary fiber supplements for weight loss and reductions in cardiovascular and cancer risks. Numerous studies, usually short-term and using purified or partially purified dietary fiber, have shown reductions in serum lipids, glucose, or insulin Jenkins et al.

Current recommendations suggest that instead of eating dietary fiber supplements, a diet of foods high in whole fruits and vegetables may have favorable effects on cardiovascular and cancer risk factors Bruce et al. Such diets are often lower in fat and higher in CHOs.

Very-low-calorie diets VLCDs were used extensively for weight loss in the s and s, but have fallen into disfavor in recent years Atkinson, ; Bray, a; Fisler and Drenick, The VLCDs used most frequently consist of powdered formulas or limited-calorie servings of foods that contain a high-quality protein source, CHO, a small percentage of calories as fat, and the daily recommendations of vitamins and minerals Kanders and Blackburn, ; Wadden, The servings are eaten three to five times per day.

The primary goal of VLCDs is to produce relatively rapid weight loss without substantial loss in lean body mass. To achieve this goal, VLCDs usually provide 1.

Introduction and context

VLCDs are not appropriate for all overweight individuals, and they are usually limited to patients with a BMI of greater than 25 some guidelines suggest a BMI of 27 or even 30 who have medical complications associated with being overweight and have already tried more conservative treatment programs. Additionally, because of the potential detrimental side effects of these diets e. On a short-term basis, VLCDs are relatively effective, with weight losses of approximately 15 to 30 kg over 12 to 20 weeks being reported in a number of studies Anderson et al.

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However, the long-term effectiveness of these diets is somewhat limited. Approximately 40 to 50 percent of patients drop out of the program before achieving their weight-loss goals. In addition, relatively few people who lose large amounts of weight using VLCDs are able to sustain the weight loss when they resume normal eating. In two studies, only 30 percent of patients who reached their goal were able to maintain their weight loss for at least 18 months. Within 1 year, the majority of patients regained approximately two-thirds of the lost weight Apfelbaum et al.

In a more recent study with longer followup, the average regain over the first 3 years of follow-up was 73 percent. However, weight tended to stabilize over the fourth year. At 5 years, the dieters had maintained an average of 23 percent of their initial weight loss. At 7 years, 25 percent of the dieters were maintaining a weight loss of 10 percent of their initial body weight Anderson et al.

It appears that VLCDs are more effective for long-term weight loss than hypocaloric-balanced diets. In a meta-analysis of 29 studies, Anderson and colleagues examined the long-term weight-loss maintenance of individuals put on a VLCD diet with behavioral modification as compared with individuals put on a hypocaloric-balanced diet. They found that VLCD participants lost significantly more weight initially and maintained significantly more weight loss than participants on the hypocaloric-balanced diet see Table Almost any kind of assistance provided to participants in a weight-management program can be characterized as support services.

These can include emotional support, dietary support, and support services for physical activity. The support services used most often are structured in a standard way. Other services are developed to meet the specific needs of a site, program, or the individual involved. With few exceptions, almost any weight-management program is likely to be more successful if it is accompanied by support services Heshka et al. However, not all services will be productively applicable to all patients, and not all can be made available in all settings. Furthermore, some weight-loss program participants will be reluctant to use any support services.

Psychological and emotional factors play a significant role in weight management.

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Counseling services are those that consider psychological issues associated with inappropriate eating and that are structured to inform the patient about the nature of these issues, their implications, and the possibilities available for their ongoing management. This intervention is less elaborate, intense, and sustaining than psychotherapy services.

For example, it should be useful to help patients understand the existence and nature of a sabotaging household or the phenomenon of stress-related eating without undertaking continuing psychotherapy. A counselor or therapist can provide this service either in individual or group sessions.

These counselors should, however, be sufficiently familiar with the issues that arise with weight-management programs, such as binge eating and purging. Short-term, individual case management can be helpful, as can group sessions because patients can hear the perspective of other individuals with similar weight-management concerns while addressing their individual concerns Hughes et al. Psychotherapy services, both individual and group, can also be useful. However, the costs of this type of service limits its applicability to many patients.

Nevertheless, the value for individual patients can be substantial, and the option should not be dismissed simply because of cost. Concerns about childhood abuse, emotional linkages to sustaining obesity fat-dependent personality , and the management of coexisting mental health problems are the kinds of issues that might be addressed with this type of support service.

The individual therapist can structure the format of the therapy but, as with counseling services, the therapist should be familiar with weight-management issues. Nonprofessional patient-led groups and counseling, such as those available with organized programs like Take Off Pounds Sensibly and Overeaters Anonymous, can be useful adjuncts to weight-loss efforts.

These programs have the advantages of low cost, continuing support and encouragement, and a semi-structured approach to the issues that arise among weight-management patients. Their disadvantage is that, since the counseling is nonprofessional in nature, the programs are only as good as the people who are involved. These peer-support programs are more likely to be productive when they are used as a supplement to a program with professional therapists and counselors.

In Overeaters Anonymous, a variant of these groups is a sponsor-system program that pairs individuals who can help one another. Certain commercial programs like Weight Watchers and Jenny Craig can also be helpful. Since commercial groups have their own agenda, caution must be exercised to avoid contradictions between the advice of professional counselors and that of the supportive commercial program.

Since the counselors in commercial programs are not likely to be professionals, the quality of counseling offered by these programs varies with the training of the counselors. Many communities offer supplemental weight-management services.

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Educational services, particularly in nutrition, may be provided through community adult education using teaching materials from nonprofit organizations such as the American Heart Association, the American Diabetes Association, and government agencies FDA, National Institutes of Health, and U. Many community hospitals have staff dietitians who are available for out-patient individual counseling Pavlou et al. However, the military's TRICARE health services contracts would need to be modified to include dietitian services from community hospitals or other community services since these contracts do not currently include medical nutrition therapy and therefore dietitian counseling.

The family unit can be a source of significant assistance to an individual in a weight-management program. For example, program dropout rates tend to be lower when a participant's spouse is involved in the program Jeffery et al. With simple guidance and direction, the involvement of the spouse as a form of reinforcement rather than as a source of discipline and monitoring can become a resource to assist in supporting the participant.

However, individual family members or the family as a group can become an obstacle when they express reluctance to make changes in food and eating patterns within the household. Issues of family conflict become more complex when the participants are children or adolescents or when spouses are reluctant to relinquish status quo positions of control. A variety of Internet- and web-related services are available to individuals who are trying to manage their weight Davison, ; Gray and Raab, ; Riva et al.

As with any other Internet service, the quality of these sites varies substantially Miles et al. An important role for weight-management professionals is to review such sites so they can recommend those that are the most useful. The use of e-mail counseling services by military personnel who travel frequently or who are stationed in remote locations has been tested at one facility; initial results are promising James et al. The use of web-based modalities by qualified counselors or facilitators located at large military installations would extend the accessibility of such services to personnel located at small bases or stationed in remote locations.

Support is also required for military personnel who need to enhance their levels of physical fitness and physical activity. All branches of the services have remedial physical fitness training programs for personnel who fail their fitness test, but support is also needed for those who need to lose weight and for all personnel to aid in maintaining proper weight.

Support services should include personnel, facilities, and equipment, and should provide practical advice on how to begin and progress through physical training routines including proper use of training equipment and how to prevent musculoskeletal injuries , as well as advice on when and how to eat in conjunction with physical activity demands.

Success in the promotion of weight loss can sometimes be achieved with the use of drugs. Almost all prescription drugs in current use cause weight loss by suppressing appetite or enhancing satiety. One drug, however, promotes weight loss by inhibiting fat digestion. To sustain weight loss, these drugs must be taken on a continuing basis; when their use is discontinued, some or all of the lost weight is typically regained.

Therefore, when drugs are effective, it is expected that their use will continue indefinitely. For maximum benefit and safety, the use of weight-loss drugs should occur only in the context of a comprehensive weight-loss program. In general, these drugs can induce a 5- to percent mean drop in body weight within 6 months of treatment initiation, but the effect can be larger or smaller depending on the individual. As with any drug, the occurrence of side effects may exclude their use in certain occupational contexts. Recognition that weight-related diseases, such as diabetes and hypertension, occur in individuals with BMI levels below 25, and that weight loss improves these conditions in these individuals, suggests that indications for weight-loss drugs need to be individualized to the specific patient.

A number of hormonal and metabolic differences distinguish obese people from lean people Leibel et al. Weight loss alters metabolism in obese individuals, limiting energy expenditure and reducing protein synthesis. This alteration suggests that the body may attempt to maintain an elevated body weight. The facts that genetics might play a role in hormonal and metabolic differences between people and that weight loss alters metabolism imply that obesity is not a simple psychological problem or a failure of self-discipline.

Instead, it is a chronic metabolic disease similar to other chronic diseases and it involves alterations of the body's biochemistry. Like most other chronic diseases that require ongoing pharmacotherapy to prevent the recurrence of symptoms, obesity management and relapse prevention may someday be accomplished through this form of treatment. The following sections provide a brief review of the mechanisms of action, efficacy, and safety of prescription agents that have been approved for weight loss and the various over-the-counter substances that are promoted for weight loss.

Energy intake may be curbed by reducing hunger or appetite or by enhancing satiety. Some obesity drugs may reduce the preference for dietary fat or refined CHOs Blundell et al. For example, the drug orlistat reduces the absorption of fat, which results in energy loss in the feces; other drugs not approved for obesity treatment reduce CHO absorption Heal et al. These drugs may produce sufficiently adverse effects, such as oily stools or increased flatus, so that patients reduce consumption of high-fat foods in favor of less energy-dense foods McNeely and Benfield, ; Sjostrom et al.

Obesity drugs also may increase activity levels or stimulate metabolic rate. Drugs such as fenfluramine or sibutramine were reported to increase energy expenditure in some studies Arch, ; Astrup et al.



Fluoxetine, although not approved for obesity treatment, has been shown to increase resting metabolic rate Bross and Hoffer, Ephedrine and caffeine, which act on adenosine receptors, may increase metabolic rate, reduce body-fat storage, and increase lean mass Liu et al. With one exception orlistat , all currently available prescription obesity drugs act on either the adrenergic or serotonergic systems in the central nervous system to regulate energy intake or expenditure Bray, b. Table summarizes the mechanism of action of pharmacological agents used for treating obesity, which are discussed in detail below.

Phentermine, an adrenergic agent, is the most commonly used prescription drug for obesity and has one of the lowest costs of all prescription agents. Weight loss is comparable with that of other single agents Silverstone, Diethylpropion, phendimetrazine, and benzphetamine are other adrenergic agents that stimulate central norepinephrine secretion and produce weight loss similar to that of phentermine Griffiths et al.

The categorization of phendimetrazine and benzphetamine as Drug Enforcement Agency Schedule III drugs may have limited their use, although little evidence exists to suggest that they have a higher abuse potential than does phentermine. Diethylpropion was reported to have a higher reinforcement potential in nonhuman primates than that of the other Schedule III and IV adrenergic drugs Griffiths et al.

No currently available agents for treating obesity are exclusively serotonergic. Fluoxetine and sertraline are selective serotonin reuptake inhibitors that produce weight loss Bross and Hoffer, ; Goldstein et al. Fluoxetine produced good weight loss after 6 months, but 1-year results were not different from those of placebo treatment Goldstein et al. Sertraline also produced short-term weight loss Ricca et al. Sibutramine inhibits reuptake of both norepinephrine and serotonin in central nervous system neurons.

Blood pressure rose slightly in normotensive subjects, but fell in hypertensive subjects Heal et al. Decreases in fasting blood glucose, insulin, waist circumference, waist-hip ratio, and computerized tomography-estimated abdominal fat were greater with sibutramine than with placebo Heal et al. The greater weight losses observed in the sibutramine group compared with the placebo group may be responsible for the greater improvements in other parameters.

Common complaints with the use of centrally active adrenergic and serotonergic obesity drugs include dry mouth, fatigue, hair loss, constipation, sweating, sleep disturbances, and sexual dysfunction Atkinson et al. Sibutramine can increase blood pressure and pulse rate in occasional patients and may cause dizziness and increased food intake Cole et al. But it rarely works out quite so simply.

One of the reasons is that, the more you exercise, the more the body naturally tries to compensate by altering your metabolism through a series of evolutionary-based protective mechanisms — first highlighted around 40 years ago — which are designed to prevent starvation and indefinite weight loss. Following exercise, a range of small but significant compensatory processes kicks in that resist the intended energy deficit. This seems to be particularly the case if a runner cuts their calorific intake at the same time as embarking on a new exercise regime.

In addition, there are certain psychological and behavioural changes that also combine to undermine attempts to shed weight. Many of us tend to overestimate the number of calories we have actually burned through exercise and increase our energy intake , either consciously or subconsciously. This is one of the reasons why some people are dismayed to find that they have put on weight despite taking up running.

Gaesser says it has been found that people who had watched promotional exercise videos tended to consume more calories than they would normally, despite having not done any exercise themselves. While, in the long term, exercise is thought to help hone our appetite regulatory system, making it easier to cut down on snacking and instead eat at set times of the day, in the short term vigorous exercise stimulates brain areas associated with reward and dependence.

This makes us crave high-fat, energy-dense foods, which can negate the beneficial effects of a running regime. It is a trend many scientists have observed by fitting runners attempting to lose weight with motion sensors or heart-rate monitors. Usually, they would naturally get in around 7, steps a day through regular activities, but during the running regime that might fall to 4,, steps. Gaesser recommends that runners wanting to lose weight invest in an activity monitor so they can check that they are still maintaining the same number of steps and overall activity when they are not running.

But it is also possible to boost your chances of burning more calories by adapting your running regime to include more high-intensity training. Some runners experience an initial boost of weight loss before finding that the rewards plateau over time, despite their best efforts.