Do Diets Work?

Does weight loss lead to long-term health benefits?

Posted Jan 01, 2014

Did you resolve to lose weight this New Year? If so, you are not alone. “Lose weight” is the #1 New Year’s resolution for 2014. Many people link weight loss with health improvements.  In fact, “Stay fit and healthy” is the #5 most popular resolution. These resolutions are supported by the weight loss industry, which has a financial interest in “helping” you make weight loss resolutions. In January we are bombarded with advertisements for diet plans and various weight loss methods. In addition to the media, people who are overweight or obese are often encouraged by their physicians to lose weight through dieting as a means of improving health. Given the emphasis on weight loss for health improvements, I think that it is important to ask: does losing weight actually lead to long-term health benefits?

Recently, a group of researchers tackled this question. In “Long-Term Effects of Dieting: Is Weight Loss Related to Health?” Tomiyama, Ahlstrom, and Mann (2013) explored the relationship between dieting, weight loss, and health outcomes. The researchers reviewed 21 previously published randomized controlled trials that examined weight loss diets with a follow-up period of at least 2 years.  They investigated health outcomes including total cholesterol, triglycerides, systolic and diastolic blood pressure, and fasting blood glucose.

The researchers found that participants in the dieting conditions lost an average of 2 pounds from starting the diet to follow-up. This was about 3 pounds more weight loss than the control condition. In addition to weight loss, the dieting groups experienced some minor health improvements, many of which would not be considered clinically significant. These health improvements are described below.

The dieters experienced a reduction in blood pressure of 2.37 mmHg for systolic and 2.71 mmHg for diastolic. This was 2.21 mmHg lower for systolic blood pressure and 0.50 mmHg lower for diastolic blood pressure than the control group.In terms of fasting blood glucose (a test used to diagnose diabetes), participants in the dieting conditions averaged a decrease of 0.05 mmol/L. Two large studies reviewed reported on the incidence of diabetes. Both reported that diabetes was significantly reduced by 58% in the dieting group when compared to a control group. Tomiyama et al. note that both of these studies included exercise in the diet group but not the control group, making it difficult to know whether diet or exercise was responsible for the reduced incidence of diabetes in the dieting groups. Participants in the dieting groups experienced small decreases in both cholesterol and triglyceride levels. Diets did not lead to any significant reductions in coronary morbidity or mortality.

The researchers then asked, were these health improvements related to weight loss? Their conclusion was NO. The authors’ analyses indicate that any health improvements that were found in the dieting groups were not related to weight loss. Some possible explanations for the improvements that the authors pose are exercise, changes in nutritional intake (ie. increased fruits and vegetables, increased fiber, decreased sodium), differences in medical care, and social support. 

So, while dieting may lead to some minimal improvements in health (many of which would not be considered clinically meaningful), these improvements are not related to weight loss. Again, it turns out that weight is not the key factor underlying health.

If you are one of the millions of Americans who will make a New Year’s Resolution today, consider “staying fit and healthy” rather than “lose weight.” Remember that the two are NOT the same! We can improve our health independent of weight loss and healthy bodies come in a diverse range of shapes and sizes. For 2014, resolve NOT to diet! Join the growing movement against dieting and sign the No Dieting Pledge here.

Reference: Tomiyama, A. J., Ahlstrom, B., & Mann, T. (2013). Long-term effects of dieting: Is weight loss related to health? Social and Personality Psychology Compass: 861-877

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