Contrary to popular belief, a new study has found that high-carb and low-fat plant-based diets do not necessarily lead to any weight gain. While this study was conducted only on a small-scale and further research is required, the findings do suggest that factors resulting in overeating and weight gain are far more complex than the amount of carbs or fat we consume in our diets.
The study conducted by the US National Institutes of Health (NIH) has been published in the journal Nature Medicine and compares low-fat plant-based diets with low-carb animal-based diets. The study observed and analysed data from a group of 20 adult participants, with researchers from the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), investigating how variation in diets affects calorie intake, hormone levels and body weight.
“High-fat foods have been thought to result in excess calorie intake because they have many calories per bite. Alternatively, high-carb foods can cause large swings in blood glucose and insulin that may increase hunger and lead to overeating,” said NIDDK senior investigator Dr Kevin Hall, the study’s lead author. “Our study was designed to determine whether high-carb or high-fat diets result in greater calorie intake.”
Over a period of four weeks, the participants, who were housed at an NIH clinical centre, were provided with either the plant-based, high-carb diet or the low-carb, animal-based diet for the first two weeks. This was then followed by the alternate diet for the remaining two weeks.
The plant-based, low-fat diet contained 10.3% fat and 75.2% carbohydrate, while the animal-based, low-carb diet was 10% carbohydrate and 75.8% fat. Both diets contained about 14% protein and were matched for total calories presented to the subjects, although the low-carb diet had twice as many calories per gram of food than the low-fat diet. The participants were allowed to choose what they ate and in as much quantity as they wanted, from the meals they were given.
Researchers found that participants who were on a low-fat, plant-based, high-carb diet consumed fewer calories than the low-carb animal-based diet. They also observed a significant loss of body fat in participants who were on a plant-based, high-carb diet, contradicting the popular belief that high-carb diets lead to weight gain.
“Despite eating food with an abundance of high glycemic carbohydrates that resulted in pronounced swings in blood glucose and insulin, people eating the plant-based, low-fat diet showed a significant reduction in calorie intake and loss of body fat, which challenges the idea that high-carb diets per se lead people to overeat. On the other hand, the animal-based, low-carb diet did not result in weight gain despite being high in fat,” explained Dr Hall.
He further said, “Our findings suggest benefits to both diets, at least in the short-term. While the low-fat, plant-based diet helps curb appetite, the animal-based, low-carb diet resulted in lower and more steady insulin and glucose levels. We don’t yet know if these differences would be sustained over a long term.”
Researchers of this study are now certain that the findings confirm weight gain and overeating to be a more complex subject than previously thought and that it goes beyond the simplistic view that weight gain is directly linked to the amount of carbs or fats one consumes. They also note that the study was not designed to make diet recommendations for weight loss and the results may have been different if participants were actively trying to lose weight.
It is also important to note that all meals for the study were prepared and provided for the participants in an inpatient setting, which may make results difficult to repeat outside the lab, where factors, such as food costs, food availability and meal preparation constraints, can make adherence to diets challenging. The researchers are, however, certain that the tightly controlled clinical environment ensured objective measurement of food intake and accuracy of data.
“To help us achieve good nutrition, rigorous science is critical and of particular importance now, in light of the COVID-19 pandemic, as we aim to identify strategies to help us stay healthy. This study brings us closer to answering long-sought questions about how what we eat affects our health,” said NIDDK director Dr Griffin P Rodgers.