- Researchers investigated the effects yo-yo dieting on the cardiometabolic health of rats by mimicking this with cycles of severe calorie restriction and refeeding.
- They found that three cycles of restriction reduced heart and kidney function and increased insulin resistance, even if rats outwardly seemed healthy.
- They concluded that yo-yo dieting could increase the risk of developing cardiometabolic disease.
Between 2017 and 2018, 73.6% of adults ages 20 and over in the United States had overweight or obesity. Having overweight or obesity is a major health concern as it increases one’s risk of conditions including:
- Type 2 diabetes
- Coronary Heart disease
- Stroke
- Gallbladder disease
- Osteoarthritis
- Sleep apnea
Weight cycling or “yo-yo dieting” happens when people intentionally lose and regain at least 5 kilograms (kg) on three occasions or more. Estimates say that between 10% and 30% of men and women have tried this kind of dieting before.
While losing weight can positively impact health, studies show that yo-yo dieting negatively impacts cardiovascular health as it causes factors including blood pressure and glucose levels to fluctuate.
Most studies investigating yo-yo dieting have focused on its short-term impacts. Studying its long-term implications could help researchers better understand the risks of yo-yo dieting.
Rat study
In a recent study, researchers studied the effects of yo-yo dieting with severe food restriction in rats.
They found that rats who underwent yo-yo dieting had reduced heart and kidney function after three dieting cycles despite “looking” healthy.
The new study was presented as an abstract at theExperimental Biology Conference on 1 Aprilby the American Physiological Society.
For the study, the researchers divided 16 rats into two groups. One group was fed a 60% reduced-calorie diet for 2 weeks followed by a 3-week period of weight regain for three cycles to simulate yo-yo dieting. The other group was kept as a control.
Throughout the study, the researchers assessed the rats’ cardiac and renal functioning via ultrasound. They also tracked their insulin sensitivity via blood tests.
After the first reduced-calorie period, the rats lost 20% of their body weight, however, this was regained during the ensuing 3-week refeeding period. The rats then lost 20% and 19% of their body weight over the next two periods of restricted calorie intake.
The researchers noted that, at the end of the study, rats on a reduced-calorie diet experienced 20–40% reductions in renal artery flow and cardiac output. They were also more insulin resistant, which is a risk factor for diabetes.
The researchers noted however that rats experienced no change in blood pressure or heart rate.
Results and possible mechanisms
When asked what may explain the findings, Aline M. A. de Souza, Ph.D., Assistant Professor in the Department of Medicine at Georgetown University Medical Center, one of the study’s authors, told MNT:
“We saw that after 3 cycles of a very restrictive diet the heart was ejecting less blood, and this means less blood going to the kidney. The body is very flexible and it tends to adjust but if it’s a chronic situation some organs can lose the adjustment ability. This is one explanation, we still need to investigate other reasons.”
As the study is yet to be published, Prof. Michael W. Schwartz, M.D., professor of Medicine at the University of Washington, not involved in the study, told MNT that he is limited in how he can interpret it.
Nevertheless, he said: ”There’s no biomedical precedent for damage to the heart or kidneys resulting from alternating cycles of caloric restriction and weight regain. With this said, it’s not clear from the summary what kind of organ damage was detected, so I hesitate to speculate further.”
“One potential factor, however, relates to the age of the animals when periods of caloric restriction began, and whether body composition was altered over the course of the study. At issue is that a 60% caloric restriction for 3 weeks is a major stress, especially for a young animal, with the potential to limit deposition of lean body mass during periods of what would otherwise be characterized as rapid growth,” he explained.
“Consequently, it’s possible that during the recovery phase, accumulation of body fat occurred preferentially over the normal deposition of lean mass during growth. If sufficiently severe, this type of process has the potential to impair organ function.”
“Moreover, if the ratio of body fat to lean mass increased as a result of reduced lean mass deposition during growth, it would also not be surprising to find that the animals end up being relatively insulin resistant, despite their comparable weight,” Prof. Schwartz added.
“Without more information, it’s not possible to do more than speculate, however,” he noted.
The researchers concluded that people who intentionally or unintentionally engage in yo-yo dieting may be at an increased risk of developing cardiometabolic disease.
When asked about potential limitations to the study, Dr. de Souza said that the sample size was small. She added that the researchers used a very specific sample too — female, young, normal body weight rats. She said that further research is needed on larger sample sizes, in humans, and in diverse demographics.
Also, as the research was conducted on rats, and not humans, it is uncertain whether the results will translate over to humans too.
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