A new study, conducted in rats and presented at the American Physiological Society annual meeting, has offered potential insights into the long-term impacts of weight-loss diets and involuntary reductions of food caused by food insecurity.

Most previous studies in humans and animals have focused on the short-term impacts of weight loss, according to researchers behind the study, but they claim less is known about how cycles of weight loss and gain may affect long-term health.

For the study, researchers divided 16 rats into two groups. One group received a normal amount of food throughout the study, while the other group experienced three cycles of a restricted diet (60 percent of their normal daily food intake) followed by three weeks of a normal diet. At the end of the study, researchers assessed the rats’ cardiac and renal functioning, as well as their insulin sensitivity.

“We found that animals going through several cycles of weight loss and body weight recovery had reduced heart and kidney function at the end. They also had more insulin resistance, which can be a cause for diabetes,” said Aline M. A. de Souza, PhD, first author of the study. “Even though the animals look to be healthy after ‘recovery’ from the diet, their heart and metabolism are not healthy.”

The findings also raise questions about public health following the COVID-19 pandemic restrictions and constantly rising food prices, which have left many without access to nutritious food. 

“Our data supports the need for additional research in people to find out if individuals who do cycles of very restrictive diets to lose weight are at higher risk of developing heart problems later in life,” said de Souza. “We still need to do more studies in this field but the findings suggest the more restrictive the diet is, the worse the health outcomes may be. Weight loss diets need careful consideration of long-term health, especially if rapid weight loss is being contemplated as an option.”

While more research is needed to determine the biological mechanisms behind the findings and determine whether the patterns observed in rats translate to people, researchers speculate that changes in calorie intake could impact biological pathways that regulate blood pressure and insulin metabolism.