The Downside of Dieting: The metabolic and health effects of calorie restriction

Written by: Kelsey Schaffstall Young MS, RDN, LDN

Are diets effective?

Research has shown that weight loss is one of the strongest predictors of weight gain. One third to two thirds of dieters regain more weight than they lost on a diet within 5 years. Although studies do show that calorie restriction can be effective in the first 6-12 months, when weight loss programs are followed for longer periods of time they tend to fail. In fact, at 2-5 year follow up weight loss programs have a failure rate of up to 95%.

What causes diet-induced weight gain?

A few major factors contribute to weight gain after dieting. First, the human body is designed to survive. In times of prolonged calorie restriction, compensatory hormone changes will occur in your body to resist weight loss and promote calorie intake.¹ For example, Ghrelin levels increase and promote hunger.¹ GLP-1 levels will decrease and reduce fullness and satiety Metabolic adaptation also occurs, meaning that resting metabolic rate decreases after weight loss, and science has shown that the decrease in RMR exceeds what would be estimated based on body composition changes.¹

The Biggest Loser Study

A 2016 study measured long term changes in resting metabolic rate in participants of “The Biggest Loser” competition. Body composition (DEXA) and RMR (indirect calorimetry) were measured at baseline, at the end of the 30-week competition, and 6 years later.

Despite substantial weight regain in the 6 years following participation in the competition, RMR remained suppressed at the same average level as at the end of the weight loss competition.^1,3 Mean RMR after 6 years was ∼500 kcal/day lower than expected based on the measured body composition changes and the increased age of the subjects.^1,3

This study showed that resting metabolic rate decreases lower than expected and metabolic adaptation persists long term after large amounts of weight loss and weight regain, which could explain why it is so difficult to maintain a lower body weight.

Common symptoms of dieting

People who diet often share a number of symptoms that stem from restriction. Body dissatisfaction and preoccupation with food and one’s body are common early symptoms of dieting which can distract from other valuable personal and health goals. Urges and cravings for “forbidden foods” can lead to episodes of binge eating and guilt which result in diminished trust in yourself around food and eating.² This distrust can lead to social withdrawal, disordered eating, and eating disorders.²

Aside from the negative experience a person may have from dieting, there are also health consequences to repeatedly losing and gaining weight, also known as weight cycling. Weight cycling has been associated with increased risk of cardiovascular disease, type 2 diabetes, hypertension, and cancer.²

A sustainable approach to healthy living

In order to minimize these symptoms, a good approach to making lifestyle changes is to make changes in your routine that you plan to keep for life. Practicing new behaviors in a small attainable way at first and adding time or repetitions once you master the habit can help make progress over time feel effortless compared to striving for drastic changes in routine. If you are struggling with negative symptoms of dieting, a Registered Dietitian with a HAES and intuitive eating approach can help you repair your relationship with food and build new habits that support your mental and physical health.

References:

1. Busetto, L, Bettini, S, Makaronidis, J et al. (3 more authors) (2021) Mechanisms of weight regain. European Journal of Internal Medicine, 93. pp. 3-7. ISSN 0953-6205
2. Evelyn Tribole M, RD, Elyse Resch M, RD, FADA. Intuitive Eating, 4th Edition: A Revolutionary Anti-Diet Approach. St. Martin’s Publishing Group; 2020.
3. Fothergill, E., Guo, J., Howard, L., Kerns, J. C., Knuth, N. D., Brychta, R., … & Hall, K. D. (2016). Persistent metabolic adaptation 6 years after “The Biggest Loser” competition. Obesity, 24(8), 1612-1619.
4. O’hara, L., & Taylor, J. (2018). What’s wrong with the ‘war on obesity?’A narrative review of the weight-centered health paradigm and development of the 3C framework to build critical competency for a paradigm shift. Sage Open, 8(2), 2158244018772888.