•  Collateral fattening is the rapid accumulation of fat that surpasses the initial set points after dieting. While the body restores lean mass slowly, excess calories prompt an increased fat storage.     
  • Contrary to popular belief, metabolism isn’t damaged; it quickly returns to its normal rate once we restore calories.


Metabolic adaptation is a big focus for researchers and competitors alike. How long does it take for your metabolism to adapt? This is a common question in the fitness community. When someone diets, their metabolic rate typically decreases due to the loss of lean mass, fat mass, and various metabolic-related hormones like leptin, thyroid, testosterone, and estrogen. People often link these signs of a slowed metabolism to extended periods of dieting. 

Researchers examined weight loss and metabolic adaptation in 94 subjects who were elite former professional soccer players from Portugal who were overweight. The weight loss study lasted four months, followed by an 8-month maintenance phase. The subjects in the active weight loss phase aimed at a moderate caloric deficit of 300-500 calories per day. The researchers also divided the subjects into metabolic phenotypes: thrifty and spendthrift.

“Thrifty” phenotypes, or metabolisms, are those whose weight loss slows down when fed fewer calories to “save” nutrients. Thrifty phenotypes also gain more weight in response to overfeeding calories. This phenotype is considered metabolically efficient and presumably engenders a risk of obesity. “Spendthrift” phenotypes, or metabolisms, are those whose metabolism slows down the least in response to the extreme diet and prefers to “spend” calories.


Spendthrift phenotype markedly increases energy expenditure in response to overfeeding but shows only a small decrease with underfeeding. Thus, compared with a subject with a thrifty phenotype, a spendthrift phenotype loses more weight with underfeeding but gains less weight with overfeeding. This phenotype seems to be protected against obesity. The researchers measured body composition, energy expenditure, and hormone levels associated with metabolic rate measured at baseline, after four months (the end of calorie restriction), and after 8 months (the end of the maintenance period).

At the end of the study, there was modest weight loss for the group. When they were dieting, the subjects had a drop in leptin and insulin, but there were no changes in thyroid hormone. The subjects lost an average of 4.3 kg or 9.49 pounds during the active weight loss phase. The average caloric deficit was estimated to be about -270 calories per day.

The former soccer players had a decrease in metabolic rate by -85 calories per day, which persisted throughout the maintenance phase. However, the decrease in players’ metabolic rate decreased to -72 calories per day. The weight loss remained constant over the year, and the players successfully lost the weight and kept it off.

Interestingly, not all players experienced the same decrease in metabolic rate. Thrifty individuals experienced greater metabolic adaptation than those classified by a spendthrift phenotype.


The thrifty phenotype individuals lost less weight (i.e., 3.5 kg or 7.7 pounds) than the spendthrift phenotype. The spendthrift group lost an average of 6.4 kg or 14 pounds. (12)

Collateral fattening, a cycle in which a person loses weight, rotating weight cycling, metabolic damage, metabolic damage recovery, is metabolic damage real, metabolic damage symptoms, what is metabolic adaptation, how to reverse metabolicadaptation

The study suggests that not all people lose weight at the same rate, and even those classified as thrifty dieters can lose weight at a slower rate. Those with thrifty phenotypes may have to do more (i.e., cut more calories and increase energy expenditure) to lose weight despite following a similar diet.

Metabolic adaptation occurs, causing slower weight loss, but metabolic adaptation is not a complete roadblock to weight loss. Metabolic rate dropped by less than 75 calories per day during the diet phase, which is relatively small and not the massive decrease in metabolic rate everyone suggests when dieting.


Today, we’re going to tackle a fascinating phenomenon known as ‘collateral fattening.’ This process occurs when our bodies, in an attempt to restore lean mass after dieting, end up depositing excess fat. By exploring this phenomenon, we aim to illuminate its implications for obesity and how understanding it can revolutionize your approach to weight management. So, buckle up and join us on this thrilling journey as we dive deep into the science of dieting and body composition, and uncover new strategies to help you achieve your weight loss goals.


Lean mass or fat-free mass drives calorie needs. Two landmark studies confirmed that daily energy intake and meal size had a positive association with fat-free mass, not fat mass. (1,2) We know that muscle loss accompanies dieting.

Fat buffers against the loss of lean muscle mass. In several studies, researchers put subjects on a restrictive diet and then allowed them to eat a caloric surplus until they restored their fat-free mass gains.

Many people around the world can lose weight, but maintaining that weight loss proves challenging. Weight cycling describes the cycle where a person loses weight and then regains it. The classic Minnesota starvation study revealed that when researchers starved lean individuals, these individuals consumed a caloric surplus until they restored their lean mass, not their fat mass.

Collateral Fattening

Such a study would be unacceptable today, but in the 1940s, researchers starved participants to the point of emaciation! They had to lose 25% of their body weight. The subjects started with a normal diet of 3,200 calories daily, then endured six months of semi-starvation with only 1,570 calories daily.

Afterward, they had a restricted rehabilitation period of three months, consuming 2,000 to 3,200 calories a day, and finally, they spent eight weeks eating without restrictions. Throughout the study, the men lost about 70% of their body fat and 18–20% of their fat-free mass.



They were gradually refed calories; they were still in a deficit compared to their baseline body composition levels (i.e., ~25% less for fat mass and 12–15% less fat-free mass). During the final 8 weeks, subjects could eat as much as possible. Their calorie intake increased by 160% of daily calorie requirements and gradually subsided to pre-weight loss levels. However, although fat-free mass had returned to pre-weight loss levels by this time, their fat mass had reached 170% of pre-weight loss values.

It takes longer for lean muscle to be restored than fat because overeating occurs, and body fat stores overshoot during this period. People keep consuming calories until lean mass is restored and their fat reservoirs overshoot. (3) A factor that influences your resting metabolic rate is lean mass and fat mass. The process of fat overshooting is what researchers have termed this “collateral fattening.”

clear glass measuring cup on white ceramic plate
People keep consuming calories until lean mass is restored and their fat reservoirs overshoot. (3)


Another example of this was a study of US Army Rangers that went thru an intense training camp and lost~25% of their body mass over 24 weeks. After 5 weeks of recovery eating, the soldier’s body fat was ~62% greater than baseline levels.

Their body fat was ~12% at baseline, which dropped to ~8% after training. Body fat increased to ~17% when they were allowed to refeed. Fat-free mass at baseline was roughly 65%; it dropped to 60% after intense training; after that, it returned to 66% upon refeeding.

The rangers ate 68% more during recovery from Ranger course training. (4) This suggests that restoring lean mass losses is a key contributor to energy intake in a caloric deficit.

Fat-free mass and resting metabolic rate are major drivers of eating. Resting metabolic rate testing equipment measures oxygen consumption and the amount of calories burned at rest. In a meta-analysis of 15 overfeeding studies, RMR and total energy expenditure increase mainly through increases in fat-free mass as weight is gained. (5) 


The “protein-stat” theory suggests food intake is regulated through the need to maintain lean mass. Losing lean tissue and the need for muscle tissue repletion after malnourishment are key variables determining appetite and meal size. (6) Restoring calories to the initial setpoint are called metabolic adaptation. How to avoid metabolic adaptation is a hot topic in the fitness community.

Diet and exercise are the two driving factors determining fat loss and lean muscle loss. Metabolic adaptation is thought to be a survival mechanism caused by excessive fat loss. RMR testing is the gold standard for measuring a slowed metabolism (i.e., burn fewer calories) caused by being in starvation mode from dieting.

Metabolic damage symptoms from long-term dieting include low body temperature, low energy or fatigue, reduced libido, loss of muscle mass, low immunity, and sleep disturbances. How to reverse metabolic adaptation is a hot topic in the fitness community.

collateral fattening
Most of the weight gain occurs thru a reduction in NEAT.


People once believed that metabolic adaptation, through decreases in metabolic rate, related to weight regain. However, this isn’t the case. When researchers compared the metabolic rate after weight regain, they found no difference.

The lead author stated, “We should put the concept of metabolic adaptation as a major driver of weight regain to rest.” (7). A reduction in NEAT causes most of the weight gain.

What is Metabolic Adaptation?

Metabolic adaptation only seems to occur when in a caloric deficit, returns with weight stability, and does not predict future weight regain. (8) A very popular method of coming out of a calorie deficit is to use a process called reverse dieting. Metabolic adaptation reverse dieting includes slowly increasing calories until you get to maintenance calories (i.e., calories to maintain weight) to avoid regaining body fat. The concept of reverse dieting makes sense, but the team at Stronger by Science feels it is a myth.

Researchers have found no long-term reductions in RMR in fitness and physique competitors. RMR reductions seem to happen during caloric restriction but return to baseline after refeeding.

Mitchell et al. discovered that natural bodybuilders didn’t experience changes in RMR during a bodybuilding show prep, even though they lost a significant amount of body fat. They attributed this to the bodybuilders’ ability to maintain lean mass throughout the show prep. (10).

In a similar case study, a female physique competitor dropped half her body fat while maintaining her lean mass. Despite the caloric drop in calories (i.e., 1040 calories) and body weight (i.e., 22 lbs.), there was only a small change in RMR. (11)  Some suggest that large increases in calories after competition increase body fat and lead to a cascade of hormones that regulate body fat, such as leptin.

When male and female bodybuilders raised their calorie intake from 1612 calories during their pre-contest diet to 1778 calories post-contest, they restored their RMR. Interestingly, body fat changes had little changes during this time, whereas there were substantial changes in lean mass (i.e., increased glycogen, fluids, electrolytes, etc.) (12)  


  • · Metabolic Adaptation doesn’t exist; the metabolic rate quickly returns once someone restores calories. Contrary to popular belief, metabolism doesn’t get damaged.
  • · After dieting, collateral fattening causes a swift increase in fat that goes beyond the initial set points. While the restoration of lean mass takes longer, the surplus calories prompt a surge in fat storage.


1.     John E. Blundell, Phillipa Caudwell, Catherine Gibbons, Mark Hopkins, Erik Näslund, and others, ‘Body Composition and Appetite: Fat-Free Mass (but Not Fat Mass or BMI) Is Positively Associated with Self-Determined Meal Size and Daily Energy Intake in Humans’, British Journal of Nutrition, 107.3 (2012), 445–49 <>.

2.     John E. Blundell, Phillipa Caudwell, Catherine Gibbons, Mark Hopkins, Erik Naslund, and others, ‘Role of Resting Metabolic Rate and Energy Expenditure in Hunger and Appetite Control: A New Formulation’, Disease Models & Mechanisms, 5.5 (2012), 608–13 <>.

3.     Abdul G. Dulloo, ‘Collateral Fattening: When a Deficit in Lean Body Mass Drives Overeating’, Obesity, 25.2 (2017), 277–79 <>.

4.     B. C. Nindl and others, ‘Physical Performance and Metabolic Recovery Among Lean, Healthy Men Following a Prolonged Energy Deficit’, International Journal of Sports Medicine, 18.5 (1997), 317–24 <>.

5.     Annemiek M. C. P. Joosen and Klaas R. Westerterp, ‘Energy Expenditure during Overfeeding’, Nutrition & Metabolism, 3 (2006), 25 <>.

6.     D. J. Millward, ‘A Protein-Stat Mechanism for Regulation of Growth and Maintenance of the Lean Body Mass’, Nutrition Research Reviews, 8.1 (1995), 93–120 <>.


7.     ‘Metabolic Adaptation Is Not a Major Barrier to Weight-Loss Maintenance | The American Journal of Clinical Nutrition | Oxford Academic’ <> [accessed 27 January 2022].

8.     Catia Martins and others, ‘Metabolic Adaptation Is an Illusion, Only Present When Participants Are in Negative Energy Balance’, The American Journal of Clinical Nutrition, 112.5 (2020), 1212–18 <>.

9.     Lachlan Mitchell and others, ‘Physiological Implications of Preparing for a Natural Male Bodybuilding Competition’, European Journal of Sport Science, 18.5 (2018), 619–29 <>.

10.  BRANDON J. ROHRIG and others, ‘Psychophysiological Tracking of a Female Physique Competitor through Competition Preparation’, International Journal of Exercise Science, 10.2 (2017), 301–11.

11.  Eric T. Trexler and others, ‘Physiological Changes Following Competition in Male and Female Physique Athletes: A Pilot Study’, International Journal of Sport Nutrition and Exercise Metabolism, 27.5 (2017), 458–66 <>.

12. Nunes CL, Jesus F, Francisco R, Hopkins M, Sardinha LB, Martins P, et al. Effects Of A 4-Month Active Weight Loss Phase Followed By Weight Loss Maintenance On Adaptive Thermogenesis In Resting Energy Expenditure In Former Elite Athletes. Eur J Nutr. 2022

About The Author

Leave a Reply