CPE Monthly: Effects of Chronic Dieting, Weight Fluctuations
By Jamie Rinaldi, MS, RDN
Today’s Dietitian
Vol. 26 No. 1 P. 38

CPE Level 2

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Metabolism encompasses the mechanisms by which the body transforms what people consume into energy to fuel all the body’s functions, producing catabolism, the degradation of molecules, and anabolism, the synthesis of new molecules.1 The metabolic rate is in direct relation to weight change. Those with the goal of losing weight can expend more calories with exercise and an enhanced metabolism that results from building muscle through strength training.2 Creating a calorie deficit by reducing calorie consumption is the more common route to weight loss; however, this isn’t sustainable long term.

The human body is designed to fight weight loss. When it’s chronically deprived of adequate calories, biological changes disrupt cues for hunger, appetite, and satiation, and energy expenditure decreases. The collection of these biological responses is referred to as metabolic adaptation and may explain why dieters plateau or regain the weight they’ve lost.3,4 RDs play a vital role in helping people achieve sustainable weight loss, given their extensive knowledge of the biological responses to weight change.

Metabolic Adaptation — A Challenge for Weight Loss
Metabolic adaptation, also called adaptive thermogenesis, is a controversial topic, with many questioning its clinical significance. Some research suggests it occurs only during the period of caloric restriction, while other studies conclude metabolism is damaged long after dieting has ceased.4-6 Several processes occur as a result of limited caloric intake, including the following:

• Hormones that regulate physical hunger and the desire to eat shift and no longer favor weight loss.

• Basal metabolic rate (BMR) drops as weight loss occurs, body fat is metabolically active (although to a significantly less degree than muscle), and loss of either or both lower resting metabolic rate (RMR).

• The thermic effect of food (TEF) declines due to reduced food intake.

• Nonexercise activity thermogenesis (NEAT) typically decreases.

• Exercise activity thermogenesis (EAT) is lower since it’s proportional to body weight

• The psychological and emotional effects of dieting also play a role.5,7-10

Hormones That Regulate Appetite, Hunger, and Metabolism
There are multiple hormones that regulate appetite, hunger, and metabolism, and it’s important for RDs to understand when hormones are released. It’s also essential for RDs to know the influence they have for educating and counseling individuals desiring weight loss (see Table 1). Knowledge of the impact of these hormones also paves the way for researchers to determine how to manipulate them for weight management.

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Caloric Restriction and Hormones
Numerous studies have been conducted to measure hormones that regulate appetite and hunger during and after calorie restriction and weight loss. Many have found increases in ghrelin and decreases in cholecystokinin, leptin, insulin, glucagonlike peptide-1, and pancreatic peptide YY, with some research showing these hormone levels persisting for six months to one year following cessation of caloric restriction. These hormonal changes may be responsible, at least in part, for dieters regaining or struggling to lose more weight.21-24 Moreover, some research has shown weight loss is associated with decreased serum triiodothyronine levels and a lower RMR.25 Studies also have found elevated cortisol levels in response to caloric restriction, triggering stress responses such as increased appetite and irritable mood that lead to weight gain.20

Total daily energy expenditure (TDEE) is comprised of BMR, the TEF, and activity expenditure, which is further divided into NEAT and EAT. The BMR is the main determinant of calorie expenditure, roughly constituting 70% of the energy spent. It’s directly related to a person’s body weight and body composition and therefore is impacted by alterations in both, resulting from weight loss or gain.4,13,26 The predominant determinant of BMR is fat-free mass (FFM), which consists of skeletal muscle, bone, organ tissue, and fluid.27

Skeletal muscle is the main component of FFM that can be manipulated, largely through strength training. Numerous studies have demonstrated a higher BMR with increased muscle mass.28,29 Furthermore, research has shown strength training to diminish skeletal muscle loss during periods of caloric restriction.30

Portions of FFM that humans can’t control during and after weight loss include the organs. Several of the body’s essential organs have a significantly higher metabolic rate than skeletal muscle and have been studied to determine if they shrink following calorie deprivation. Research is limited; however, it has shown decreased sizes of the liver, spleen, and kidneys as a consequence of weight loss, thereby contributing to a lower BMR.31,32

Determining a person’s BMR can be instrumental in establishing an appropriate calorie intake goal to promote weight loss. RDs can estimate a client’s BMR using the Harris-Benedict or Mifflin-St. Jeor equation, or direct the client to a practitioner who can more accurately measure BMR via direct calorimetry, indirect calorimetry, a whole-room respiratory chamber, metabolic carts, or the doubly-labeled water technique.26

The TEF, also termed postprandial thermogenesis, is the increase in metabolism following calorie consumption and comprises approximately 10% of energy expenditure. The TEF provides the energy needed to digest and metabolize food. It’s primarily regulated by the total number of calories consumed and therefore is lowered with calorie restriction.13,26,33

It has been previously hypothesized that small, frequent meals would produce a greater overall calorie burn through TEF than three meals per day. Dieters also have been encouraged to consume breakfast to stimulate metabolism; however, research on these concepts has produced contradicting conclusions, and many studies have shown negligible effects of altering meal timing and frequency.33-36

Energy burned with movement outside of planned exercise, termed NEAT, is widely variable from one person to another and can be upwards of 2,000 calories per day for two people of the same weight, depending on their habits and lifestyles. The difference in total energy expenditure in two individuals of the same size and with the same body composition is mainly due to their activity expenditure, primarily NEAT, as it encompasses all movement throughout the day other than workouts, for example, fidgeting, vacuuming, singing, and adjusting posture. NEAT varies not only from person to person but also seasonally—people tend to be more active
in warmer months, for instance.37-39

The reduction in NEAT due to advances in technology—especially those that are labor saving—has made a significant contribution to obesity, both at home and in the workplace. Moreover, studies have demonstrated that an inadvertent decrease in NEAT with calorie deprivation and weight loss, and without recovery, could make weight maintenance unrealistic.37-39 Health practitioners placing a conscious focus on NEAT may play a key role in weight management.39

The other component of physical activity is EAT, or planned exercise. Data obtained from the National Weight Control Registry show that 94% of participants exercise regularly as part of their weight loss plan, and 90% continue to exercise to support weight maintenance. Much of the research confirms the contribution of a regular exercise routine to weight management; however, a large part of the population remains sedentary.40 According to the CDC, fewer than 25% of American adults meet the recommended aerobic and strength-training guidelines.41

When counseling individuals with the goal of weight loss and maintenance, RDs and other health practitioners should advise habitual cardiovascular exercise and resistance training as part of the plan. At a lower body weight, fewer calories are expended when performing the same exercises, and weight watchers need to be informed that they will need to increase exercise intensity and/or duration for continued progress as they lose weight.13,38,40

Weight Cycling and the Set Point Theory
Yo-yo dieting, also known as weight cycling, is defined as repeatedly losing weight and then regaining it. In the absence of a good strength training program, the regained weight is primarily fat, therefore, at the same weight, RMR is lower. As this and other biological responses, such as the hormonal shifts that drive an increase in calorie intake, repeatedly occur, losing weight becomes increasingly less achievable.3,42,43 Observational research, while less reliable than other studies, confirms the challenge dieters face as weight decreases.44

The Set Point Theory hypothesizes that the human body fights for body weight homeostasis and presents another challenge for individuals desiring to lose weight. According to this theory, biological reactions to weight loss are intended to keep weight at a set point or within a set range.3,44,45 This theory is consistent with the body’s response to starvation, which evolved in early humans to survive periods of famine.46,47

Obesity researcher Ethan Allen Hitchcock conducted an overfeeding study in the 1960s, using 20 normal weight inmates from Vermont State Prison as his subjects. The prisoners were fed up to 10,000 kcal per day for four to six months to promote weight gain, and all gained between 20 and over 40 lbs. All but two of the subjects lost all of the weight they had gained in a relatively short period of time once they resumed their regular eating patterns, supporting the set point model.48,49 George Bray, also an obesity researcher, duplicated the experiment on himself and four volunteers in the early 1970s and showed the same results: all five subjects rapidly returned to their usual weights once the overfeeding period ended.48 Studies in identical twins raised separately have shown they share similar weight patterns despite not being in the same environment, suggesting weight is genetically determined.49

Adipose Tissue
The adipocytes of white fat tissue aren’t lost with weight loss, but rather they shrink, leading to multiple biological processes that favor weight gain.50 White adipose tissue is intended to store energy. Conversely, brown adipose tissue—and possibly beige fat as well—burns energy; therefore, increasing it may be useful in promoting weight loss.51,52 Research has shown increases in brown adipose tissue, beige adipocytes, thermogenesis, and weight loss in subjects chronically exposed to temperatures cold enough to provoke shivering; however, this may not be a practical suggestion for dieters.53,54 Studies have displayed the same benefits from consuming certain food components, with the most promising ingredient being capsinoids, found in chili peppers. Curcumin, resveratrol, menthol, omega-3 fatty acids, and green tea catechins also may exert the same effects.51-54 RDs can guide dieters in incorporating some or all of these food constituents into their diets.

The Microbiome
Emerging research shows that obese individuals lack much of the “good” gut bacteria that lean people have, which could be interpreted as evidence that a healthier gut microbiome may favor weight loss. Studies also suggest caloric restriction alters gut microbiota in obese subjects to match that of lean individuals.55-58 Changes in diet composition also can improve the quality of the gut microbiome, most notably the inclusion of prebiotics and probiotics and the avoidance of foods high in fat and sugar.59 Nutrition professionals can educate weight watchers on the specific foods to consume or eliminate from their diet.

Psychological and Emotional Factors
The effects of chronic dieting reach beyond physiology, eliciting cognitive changes that make weight maintenance challenging, for example, a preoccupation with food. In severe cases, caloric deprivation, self-imposed or not, paves the way for eating disorders such as bulimia nervosa and binge eating disorder. Changes in the brain also can heighten senses, making food more enjoyable and making individuals view food as a reward.7

Studies have shown psychological and emotional effects of calorie deprivation and their interference with sustained weight loss. Dieters may suffer from depression, feel unmotivated, and have difficulty concentrating or making decisions. Weight loss subjects also have reported a diminished sex drive, body image distortion, and the feeling of being out of control.7,60

The Minnesota Starvation Experiment
The Minnesota Starvation Experiment was a study of the physical and psychological effects of semistarvation that simulated famine in 36 volunteers at the University of Minnesota between 1944 and 1945. The subjects were healthy white males aged 22 to 33. The first three months of the study were a baseline phase; caloric prescriptions were individualized so the volunteers could attain their ideal body weight for height. For six months following this control period, calories were limited to <1,600 to 1,800 kcal, mimicking famine in Europe during World War II. Refeeding took place during the final three months of the study. By this time, only 32 men were still in the study, and they were divided into four groups to investigate the effects of different calorie levels on the rate of physical and psychological rehabilitation. Throughout the study, subjects were assigned physical activities in excess of what humans would naturally perform, including the requirement to walk ~35 km per week (~22 miles).60,61

The experiment took a profound toll on the bodies and minds of the men who participated in the study. During the semistarvation period, subjects were exhausted, irritable, and preoccupied with food. They all lost significant fat and muscle mass, leaving them with protruding ribs and a mean BMI of 16.4—the mean BMI during the control period was 21.9. During the refeeding period, the men gained back more fat than they had lost, and it wasn’t until several months afterward that they regained their lost strength. Their emotional and mental states didn’t improve until weeks into refeeding.60-62

A brief (six weeks) version of this experiment, focused on the physiological consequences of weight loss, was repeated in 2012 at the Christian Albrechts University, again with 32 healthy young men. Calories were restricted to approximately 50% of weight maintenance needs to promote weight loss. Adaptive thermogenesis occurred soon after the onset of caloric restriction and persisted throughout the semistarvation period; however, metabolism recovered within two weeks of resuming usual eating patterns, during which the subjects consumed balanced diets of 15% protein, 50% or 65% carbohydrate, and 20% or 35% fat. For both the calorie restriction and initial refeeding periods, 50% of calories came from a liquid formula to standardize what the participants were eating. Conclusions from this study may be more reliable given the improved technology to measure energy expenditure, body composition, and circulating hormones that affect weight and appetite. It’s likely that the same results can be reproduced in others who temporarily cut calories to produce sustainable weight loss, going against the notion of a permanently “damaged” metabolism.63 RDs and other health professionals can use this information to educate and motivate clients who struggle with losing and maintaining weight.

The Biggest Loser
The Biggest Loser was a televised weight loss competition that required participants to restrict their calorie intake to 1,200 to 1,600 kcal and exercise for four to eight hours every day. It premiered in 2004 and was canceled in 2016 due to poor publicity. News headlines claimed metabolic adaptations continued for six years following participants’ weight loss after a peer-reviewed journal article was published in Obesity. A letter to the editor published later that year in the same journal pointed out the flawed methods, which led researchers to conclude that “persistent metabolic adaptation” was still present six years after weight loss.6,64 RDs have the responsibility of analyzing the research to properly inform their clients and the public of falsehoods and facts about weight management in the media. In The Biggest Loser study—for example, different methods, some unvalidated—were used to measure the contestants’ BMR at the time of the study and again six years later, making the data questionable. In addition, only 16 contestants were included in the study, also making it unreliable due to such a small group of people.64

Preventing or Repairing a ‘Damaged’ Metabolism
A damaged metabolism is one that has slowed to the point of making weight loss extremely difficult or impossible. This slowing of RMR is believed by many scientists to exceed the expected damage with the change in body composition and can be permanent; however, other researchers have disputed this notion.65 There are multiple approaches with the potential to prevent or reverse the metabolic harm attributed to prolonged calorie restriction. Although whether or not permanent damage to metabolism from losing weight remains a controversial topic, health practitioners can equip those wishing to maintain weight loss with numerous promising methods focused on dietary changes and regular exercise for success.

High Protein Diet/The PREVIEW Study
A high protein diet may attenuate some of the metabolic adaptations that accompany weight loss. One reason for this is that protein requires a significantly greater amount of energy to digest than carbohydrate or fat, thereby increasing postprandial energy expenditure to a larger extent. Protein is also satiating, allowing for a calorie deficit without feeling deprived and without the effect on hormones that induce appetite and hunger. This macronutrient supports the maintenance of lean muscle mass, helping preserve metabolism.66,67

The Preview Study was a randomized clinical trial conducted in eight different countries over three years with 2,326 adults aged 25 to 70. An eight-week weight loss period was followed by a 148-week weight maintenance stage. Researchers assigned men and women to two different macronutrient ratios: 25% protein, 30% fat, and 45% carbohydrate (“high protein”), or 15% protein, 30% fat, and 55% carbohydrate (“moderate protein”). The study concluded that the high protein diet mitigated the adaptive thermogenesis that occurs with weight loss, increased energy expenditure, and created a negative energy balance when compared with the moderate protein diet.68 RDs can recommend a higher protein intake for clients seeking weight loss if it’s realistic and not clinically contraindicated; this approach doesn’t suit everyone. A diet high in protein may worsen certain chronic health conditions, such as renal or liver disease. High protein intake also may be harmful to healthy adults, with some studies suggesting an increased risk of cancer, acceleration of CVD, and bone disorders.69

Intermittent Fasting
Intermittent fasting (IF), also known as intermittent energy restriction, alternates periods of fasting or consuming very few calories with unrestrained eating. There are an infinite number of possible IF diets. The 5:2 diet, for example, involves five days of ad libitum eating followed by two days of fasting or severely limiting calorie intake. A variation of the 5:2 diet is alternate-day fasting, where a one-day fast may separate any number of days of unrestricted food consumption. Another common approach to IF, time-restricted eating (TRE), is having a window of time each day, most commonly eight hours, within which one can eat freely. The other 16 hours are spent fasting. Most individuals using IF to lose weight instead of a traditional low-calorie diet do so because it’s seemingly more tolerable mentally and physically; however, there are other potential benefits. Intermittent energy restriction may counteract the undesirable hormonal shifts and the decline in RMR that occur with a traditional diet.70,71

In one eight-week study, 34 male subjects who regularly lifted weights were divided into two groups: one group followed the TRE method of weight loss, permitted to eat within an eight hour window, while the others spread their meals throughout the day. Both groups maintained their FFM, but the TRE subjects also had a decrease in their fat mass, supporting the theory that IF may preserve metabolism despite caloric restriction.72

The HELENA Trial was a randomized controlled trial that studied 150 overweight adults for 50 weeks. The intervention phase lasted 12 weeks, followed by a 12-week maintenance period and 26 weeks of follow-up. The adults were divided into three groups: the IF group, the continuous calorie restriction (CCR) group, and the control subjects. During the intervention phase, both the IF and CCR participants consumed 80% of their energy requirements for weight maintenance. This 80% was a weekly average for the IF group—they each chose two days, not in a row, on which they consumed 75% of their calorie needs, while they were unrestricted for the other five days. The CCR subjects were restricted to 80% of their daily calorie requirements. There were no significant differences in amount of weight loss, body composition change, or biomarkers of metabolism between the IF or CCR subjects.73 Although this research doesn’t support IF as a superior route to weight management, it was just as effective and perhaps would be more appealing to clients than daily caloric restriction. Furthermore, other versions of IF may produce more favorable results.

Researchers reviewed randomized controlled trials comparing IF to CCR conducted between 2009 and 2019. The most common IF methods were the 5:2 diet and alternate-day fasting. The review concluded that IF is more successful than CCR in producing weight loss and protecting metabolism; however, RDs shouldn’t recommend this for everyone as it may not be appropriate in some populations, such as those with type 1 diabetes or women who are pregnant or breastfeeding.71 Healthy individuals who suffer the psychological and emotional effects of traditional weight loss diets likely would benefit the most from IF.

Calorie Cycling
Calorie cycling, also called calorie shifting, is another promising method of preserving metabolism while still losing weight. Like IF, there are unlimited ways to cycle calories; however, all involve days of adhering to different calorie levels. Athletes or individuals who exercise regularly tailor the calorie cycling to their workouts. More calories, primarily in the form of carbohydrate, typically are consumed on days of strength training and/or more intense exercise. A study of 26 athletes who underwent 12 weeks of calorie restriction followed by a one-week “diet break” showed improved training performance and endurance during the higher calorie days, potentially resulting in increased muscle mass, RMR, and calorie expenditure. This study also demonstrated increased satiety, reduced feelings of hunger, decreased irritability, and enhanced alertness during the higher calorie days. The combined physiological and psychological impacts of liberalizing caloric intake may be effective in reversing metabolic adaptations to weight loss diets.74,75

Another study of 74 women struggling with their weight compared the effects of calorie cycling with those from CCR. All subjects had similar amounts of weight loss during the study; however, the women who cycled calories were more successful with maintaining weight loss, and their metabolic rates had returned to prestudy levels, while those in the CCR group had significantly reduced BMRs. Another important factor for health professionals to emphasize to clients is that the calorie cyclers felt much less deprived than those who restricted calories on a daily basis.75 As the research on calorie shifting demonstrates favorable physiological and psychological effects, it’s also advisable to weight watchers who poorly tolerate CCR.

Both aerobic exercise and resistance training have the potential to offset hormonal and metabolic changes that occur with weight loss. Some studies have shown reductions in appetite as a response to aerobic exercise, possibly due to the impact of physical activity on circulating hunger hormones.76 High-intensity training, whether cardiovascular or strength training, is well known to result in excess postexercise oxygen consumption, elevating the metabolic rate for some time even after the workout is complete.77,78 There’s also strong evidence showing an increase in RMR following weeks or months of regular strength training due to preservation or an increase in muscle mass.28,29,79,80

A randomized trial of 32 previously sedentary women compared the effects of two workouts (cardiovascular) per week to six workouts per week without controlling diet. It was previously known that humans often naturally compensate for aerobic exercise by eating more. In this study, the subjects who exercised six times per week increased their calorie consumption approximately the same amount as those who exercised twice per week, primarily attributed to shifts in circulating leptin and ghrelin, and experienced greater weight and fat loss. Researchers estimated that 300 minutes of exercise per week is ideal for weight loss.81

To achieve weight loss and management with exercise, it would be prudent for RDs to advise a combination of cardiovascular and strength training. Although much research suggests aerobic exercise is more effective than resistance training for weight loss, strength training is likely beneficial for preserving or improving BMR.40

Reverse Dieting
Reverse dieting is gradually, and in modest increments, increasing calories to recover hormone levels that support weight maintenance and increase RMR, essentially reversing the metabolic adaptation to weight loss. Research on reverse dieting is limited and primarily focuses on athletes and bodybuilders following a “cut” phase. Carbohydrate and fat intake are lowered during the cut period and then are reintroduced slowly and methodically to increase metabolism without significant gain of fat mass. Calories are typically increased by 2% to 3% per week while weight and body composition are monitored regularly.

Reverse dieting may have a place in restoring metabolism in nonathletes who have lost weight and want to avoid an excessive rebound gain in response to discontinuing caloric restriction.82,83 The downside of reverse dieting is the need for strict adherence to a calorie-controlled diet with continuous monitoring of intake and body measurements. Less-educated individuals and those who want more dietary flexibility likely wouldn’t be successful with a reverse diet. What’s more, such a rigid plan may be emotionally and physically damaging to those with a history of or active eating disorders.

Putting It Into Practice
The human body is designed to resist weight loss. Long-term calorie restriction triggers multiple biological processes that make the body more efficient with fewer calories, a development termed metabolic adaptation, which is thought to be traced back to human evolution as a survival strategy during periods of starvation. Hormones stimulate appetite and hunger and calorie expenditure in response to BMR, the TEF, NEAT, and exercise. The result is weight regain after the weight loss diet ends or a plateau while still restricting calories. Many people don’t understand the physiological and psychological factors that influence the cessation of weight loss and how to respond and become frustrated.

RDs are instrumental in guiding clients using one or more of the aforementioned techniques to prevent or reverse metabolic adaptation. Where clinically appropriate, increasing protein intake may be the easiest way for clients to minimize metabolic damage, especially due to its satiating effect. RDs also may advise IF for weight watchers who feel deprived with traditional weight loss diets. Calorie cycling and reverse dieting are emerging as other potential ways to protect metabolism; however, these are more complex, and the purported benefits have been studied only in athletes and bodybuilders. With the exception of those who are physically unable to participate in an exercise program, regular workouts are universally advisable for offsetting the negative consequences of calorie restriction and weight loss. However, there’s no one-size-fits-all protocol when it comes to a weight management regimen. RDs should consider each client’s preferences, tolerances, routines, and whatever else may impact their lifestyles when tailoring a weight loss program to each individual.

— Jamie Rinaldi, MS, RDN, has a master of science in Applied Physiology and Nutrition and has been practicing since 2001. She’s a regional dietitian for Nutrition Management Services and a writer for SoulFIRE Health, a website that provides educational materials to be used by dietitians, health coaches, and other clinical professionals.


Learning Objectives
After completing this continuing education course, nutrition professionals should be better able to:
1. Distinguish the primary hormones that affect hunger and appetite.
2. Define adaptive thermogenesis.
3. Evaluate the role of the gut microbiome in weight management.
4. Analyze the research on dieters years after they’ve lost a significant amount of weight.


1. Which of the following is a consequence of weight loss?
a. Reduced hunger due to hormonal shifts
b. Increased basal metabolic rate
c. A decreased thermic effect of food
d. Depression

2. Which hormone stimulates hunger?
a. Leptin
b. Ghrelin
c. Cholecystokinin
d. Pancreatic peptide YY

3. What study had profound psychological and emotional consequences from calorie deprivation?
a. The Vermont Prison Study
b. The Biggest Loser Study
c. The HELENA Trial
d. The Minnesota Starvation Experiment

4. An increased intake of what nutrient was shown to counteract adaptive thermogenesis in the PREVIEW study?
a. Protein
b. Iron
c. Fat
d. Fiber

5. Studies of what population suggest weight is genetically predetermined?
a. Native Americans
b. Identical twins
c. Fraternal twins
d. Teenagers

6. Which weight loss method is advisable for those who feel deprived on traditional weight loss diets?
a. Continuous calorie restriction
b. Aerobic exercise
c. Reverse dieting
d. Intermittent fasting

7. By how much are calories increased per week with reverse dieting?
a. 100 to 200 kcal
b. 5% to 6%
c. 2% to 3%
d. 2% to 3% + 250 kcal

8. Which of the following contributes the most to energy expenditure?
a. The thermic effect of food
b. Nonexercise activity thermogenesis
c. Exercise activity thermogenesis
d. Basal metabolic rate

9. What component of energy expenditure can vary by up to 2,000 kcal per day for two people of the same weight and body composition?
a. The thermic effect of food
b. Nonexercise activity thermogenesis
c. Exercise activity thermogenesis
d. Basal metabolic rate

10. Which type of weight loss plan may be inappropriate for individuals with type 1 diabetes?
a. Continuous calorie restriction
b. Aerobic exercise
c. Reverse dieting
d. Intermittent fasting


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