May 2017 Issue

Overweight/Obesity: Potential Perils of Weight Cycling
By Carrie Dennett, MPH, RDN, CD
Today's Dietitian
Vol. 19, No. 5, P. 18

Why 'Yo-yo Dieting' May Lead to Weight Gain and Harm Cardiometabolic Health

Weight cycling, repeated cycles of intentional weight loss and unintentional regain, is common among dieters. Also known as "yo-yo dieting," weight cycling is characterized by metabolic adaptation to weight loss, something that served our ancestors well during times of feast and famine,1 but not so much in today's modern food environment. Does this formerly beneficial adaptation to the environment now predispose people to weight gain and cardiometabolic risk?

How Common Is Weight Cycling?
The prevalence of dieting has increased in recent decades, along with the number of people categorized as obese, according to the BMI charts.2 In spite of that, most dieters don't maintain their losses—an estimated 80% of individuals who intentionally lose more than 10% of their body weight will regain that weight within a year.3,4 This makes weight cycling common, although exact estimates vary between studies, from 20% to 55% among women and 20% to 35% among men.2

Dieting and weight cycling aren't limited to those with an overweight or obese BMI classification. Many adults, adolescents, and children with normal or even underweight BMIs diet because they think they weigh too much or feel pressure from society, media, or friends and family.2 National Health and Nutrition Examination Survey data show that the percentage of normal-weight individuals who made some effort (ie, diet and/or physical activity) to lose weight increased between the mid-1990s and 2003 to 2008, from 37% to 46% for women and from 11% to 19% for men; 13.5% of underweight women also pursued weight control.5 In addition, athletes in "weight sensitive" sports, where adhering to aesthetic standards or weight categories is necessary, may weight cycle between seasons. Because these sports may start at a young age, weight cycling is observed even in adolescent athletes.2

Why Weight Cycling Occurs
The most common reasons why weight cycling occurs in adult men and women and among youths include the following:

• Food environment. Dieting and restriction increases the reward value of food, leading to overeating or even binge eating—a common vulnerability in our modern food environment.6 Michael Lowe, PhD, a professor in the department of psychology at Drexel University in Philadelphia, says there are two reasons why even people who lose large amounts of weight may regain. "One is that having a predisposition toward weight gain continues to manifest itself in an obesogenic environment because we have an almost unlimited capacity to gain weight if the food environment encourages it. The second is that the act of weight loss unleashes additional biological and appetitive forces that push weight back to where it was."

• Weight overshooting. Weight loss reduces both fat and fat-free (lean) body mass while producing metabolic shifts that favor lipid storage,7 so fat overshooting (when fat regain exceeds the amount lost) is necessary to allow complete recovery of lean mass during weight regain.8 Overshooting after each cycle of weight loss and regain can contribute to future weight gain and possibly obesity.7

Adaptive thermogenesis. Thermogenesis (the burning of calories to produce heat) declines with weight loss and stays depressed during regain because of drops in energy expenditure at rest and during activity.9 The drop in energy expenditure is paired with an increased drive to eat, which both animal and human studies show leads to overeating when free access to food is allowed.7,10,11 This increased hunger and appetite is triggered by loss of lean mass, and contributes to fat overshooting.8

Adaptive response to the food supply. One proposed model for weight cycling suggests that uncertainty about food supply with dieting and food restriction triggers an adaptive response to gain weight, similar to what our early ancestors would have experienced during times of variable abundance and scarcity. Recurrent attempts to diet may lead to greater fat storage between diets than if the individual was never restricting food.12

How Weight Cycling Affects the Body
Does weight cycling lead to weight gain and increased risk of cardiometabolic diseases (eg, type 2 diabetes and cardiovascular disease) compared with expectations if someone remained overweight or obese without dieting? Scientific research has yielded mixed results, in part due to varying definitions of weight cycling.13,14 Some dieters may experience one large weight cycle, while others may experience repeated smaller cycles.2

Dieting, especially repeat dieting, is a predictor of future weight gain, especially among younger dieters who start out lean.2,8 A 2012 study that followed 4,129 mostly normal-weight teenage twins into young adulthood found that the more frequent the weight cycling, the greater the increase in BMI and risk of becoming overweight. This association was strongest among teenage males who started in the lowest BMI category.15 A 2013 study involving 950 female twins aged 18 to 60 found that younger age at dieting onset was associated with an increase in BMI, risky dieting behaviors, and episodes of weight cycling.16

However, it's unclear whether the upward weight trend seen with weight cycling is due to dieting itself, or because individuals who diet repeatedly are trying to "outrun" a genetic predisposition to obesity.8 Among normal-weight individuals, those who are gaining weight are more likely to diet than those who aren't gaining.17 However, one study found that healthy young men who lost 12% body weight during a rigorous eight-week army training course regained more weight—especially more fat—than they lost.8,18

A 2015 review coauthored by Abdul Dulloo, PhD, a professor in the department of medicine/physiology at the University of Fribourg in Switzerland, suggests that lean dieters are at greater risk for of overshooting than overweight or obese dieters. The lower the dieter's initial body fat percentage, the higher the proportion of lean mass lost and the higher the proportion of fat mass gained.8,19 Studies of overweight or obese dieters undergoing one to three weight cycles don't show significant alterations in body composition over time, but in dieters who start out lean, cumulative fat overshoot over several weight cycles may add up to a substantial increase in body fat.8,20

"Our analysis suggests that it is weight cycling resulting from repetitive intentional weight loss in primarily normal-weight population groups that's more strongly associated with disease risks," Dulloo says. "The most significant health concerns being increased weight gain and greater risk of the development of type 2 diabetes, hypertension, and coronary heart disease."

Also concerning is that dieting older adults are more likely to regain fat than muscle and may not fully regain that muscle. Over time, especially with weight cycling, this could exacerbate sarcopenic obesity (low muscle mass with high fat mass),21 leading to physical limitation and risks to cardiometabolic health.22-24 Along with fat overshoot, weight cycling can cause overshoot of blood pressure, heart rate, blood glucose, lipids, and insulin2 while depressing levels of HDL cholesterol in women.25 Weight cycling also contributes to chronic inflammation,7,25 and weight cycling that results in weight gain above baseline may pose a strong risk of developing type 2 diabetes compared with noncycling.26

Strategies for Dietitians
If weight cycling poses the most risk for normal BMI dieters, how should dietitians respond to these clients?

"A person who fits the thin ideal of our culture and appears to have a normal weight and still desires to lose weight at best has a body image issue; at worst, it could be a mental health problem—like an eating disorder or body dysmorphic disorder," says Rebecca Scritchfield, RDN, HFS, a Washington D.C.-area dietitian and author of Body Kindness.

For all clients, she suggests leaving weight off the table and instead focusing on habits, letting weight adjust naturally. "Health and happiness are most likely to improve with optimism and empathy for self-care habits," she says. "Science doesn't show benefits to calorie counts. Restriction (even if not calories but foods—think the Whole30 diet) leads to anxiety about food and overeating."

Public health messages may be fueling this anxiety, Dulloo says. "Terms like 'war on obesity' and obsession about slimness can backfire over the long term, as suggested by several prospective studies indicating that dieting or attempts to lose weight during childhood and adolescence predicts future weight gain and obesity." What does he suggest instead? "The emphasis should not be about 'body weight' or 'body fat' per se, but about motivation for a healthy lifestyle in relation to food and physical activity."

Lowe agrees, especially regarding the current food environment. "Long-term weight loss is possible in a small minority of people, but if the focus is on public health, I think society should be investing far more in prevention than in treatment," he says. "In the current environment, most young children will become overweight or obese at some point in their lives.

— Carrie Dennett, MPH, RDN, CD, is the nutrition columnist for The Seattle Times and speaks frequently on nutrition-related topics. She also provides nutrition counseling via the Menu for Change program in Seattle.

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