Is Yo-Yo Dieting Really Harmful? What Science Says

Many people regain weight after dieting, leading to concerns about yo-yo dieting and its impact on health. While some animal studies suggest risks, human research finds no strong evidence that weight cycling harms health. Experts recommend focusing on waist size and fat distribution rather than just BMI for a more accurate health assessment.

Is Yo-Yo Dieting Dangerous? Here’s What Science Says

January 30, 2025: Many people struggle with maintaining weight loss. They diet, lose weight, and then gain it back—a cycle known as yo-yo dieting. This has led to concerns that repeated weight loss and gain may be harmful. But is that really true?

A recent review of scientific studies found no strong evidence that yo-yo dieting is harmful to health. In fact, experts suggest that trying to lose weight even if it’s regained is better than never attempting weight loss at all.

What is Yo-Yo Dieting?

Yo-yo dieting, or weight cycling, refers to the repeated loss and regain of weight. Concerns about its risks first emerged from animal studies, where starving and refeeding obese rats showed negative health effects. This led to widespread media reports warning about the dangers of weight cycling.

However, animal studies do not always apply to humans. In fact, some studies on mice show that weight cycling can actually extend lifespan. More importantly, human research does not confirm serious health risks from yo-yo dieting.

Is BMI the Right Measure of Obesity?

Many people rely on Body Mass Index (BMI) to determine whether they are overweight or obese. However, BMI does not consider body fat percentage or fat distribution. For example, bodybuilders may have a high BMI but very little fat.

According to the World Health Organization (WHO):

• Men with over 25% body fat and women with over 35% body fat are considered obese.
• In the 1990s, only 20% of Americans were classified as obese based on BMI, but research shows the real number was closer to 50%.

Since BMI can misclassify people, doctors may fail to identify individuals who are at risk due to excess body fat.

Why Waist Size Matters More Than BMI

Experts now say that waist size is a better indicator of health risks than BMI. This is because visceral fat, the fat stored around organs, is more dangerous than the fat under the skin.

• A waist size of 31.5 inches (80 cm) or more in women and 37 inches (94 cm) or more in men increases health risks.
• The risk becomes serious when waist size exceeds 34.5 inches (88 cm) in women and 40 inches (102 cm) in men.
• A man with a waist size over 43 inches (110 cm) has a 50% higher death risk, while a woman with a 37.5-inch (95 cm) waist has an 80% higher risk.

The Good News: Visceral Fat is Easy to Lose

The most dangerous type of fat—visceral fat—is also the easiest to lose. Even a small weight loss can provide significant health benefits:

• Losing just 3% of body weight improves blood sugar and triglycerides.
• Losing 5% improves blood pressure and cholesterol levels.
• A 5% weight loss can reduce the risk of diabetes by 50%.

For example, someone weighing 90 kg (200 lbs) only needs to lose 4.5 kg (10 lbs) to see health improvements.

What Should You Do?

• Don’t rely only on BMI—check your waist size too.
• Avoid extreme dieting—instead, focus on gradual, sustainable weight loss.
• Stay active and eat a balanced diet to maintain weight loss.

Conclusion

Yo-yo dieting may not be as harmful as once believed. In fact, losing weight—even temporarily—is better than never trying at all. Instead of focusing only on BMI, measuring waist size and reducing visceral fat should be a priority. Sustainable lifestyle changes, rather than extreme diets, offer the best long-term health benefits.

Source: https://nutritionfacts.org/blog/an-ideal-waist-size/ (Read in detail) Author: Michael Greger M.D. FACLM (Dr. Greger is a physician, New York Times Best-Selling author, and internationally recognized speaker on nutrition, food safety, and public health issues.)