News release
Thursday January 21, 2021
People on a low-fat, plant-based diet ate fewer daily calories, but had higher insulin and blood glucose levels, compared to when they ate a low-carb, animal diet, according to a small but very controlled study at the National Institutes of Health. Led by researchers at the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), the study compared the effects of the two diets on calorie intake, hormone levels, body weight, and more. The findings, published in Nature Medicine, a better understanding of how restricting carbohydrates or fats in the diet can affect health.
“High-fat foods are thought to lead to excessive calorie intake because they contain many calories per bite. Alternatively, high-carbohydrate foods can cause large swings in blood glucose and insulin that can increase hunger and lead to overeating, ”said NIDDK Senior Investigator Kevin Hall, Ph.D., the study’s lead author. “Our study was designed to determine whether high-carbohydrate or high-fat diets result in increased calorie intake.”
The researchers housed 20 adults without diabetes for four consecutive weeks in the Metabolic Clinical Research Unit at the NIH Clinical Center. The participants, eleven men and nine women, were fed a plant-based, low-fat or low-animal carbohydrate diet for two weeks, immediately followed by the alternative diet for two weeks. The low-fat diet was rich in carbohydrates. The low-carbohydrate diet was rich in fats. Both diets were minimally processed and contained equivalent amounts of non-starchy vegetables. The participants were given three meals a day, plus snacks, and were allowed to eat as much as they wanted.
The main results showed that people on a low-fat diet ate 550 to 700 calories less per day than when they followed a low-carbohydrate diet. Despite the wide differences in calorie intake, the participants reported no differences in hunger, meal enjoyment, or fullness between the two diets. Participants lost weight on both diets, but only the low-fat diet resulted in significant body fat loss.
Despite eating foods abundant in high glycemic carbohydrates that resulted in marked fluctuations in blood glucose and insulin, people who ate the plant-based, low-fat diet showed significant reductions in calorie intake and loss of body fat, which challenges the idea. that high-carb diets in themselves lead to people overeating. On the other hand, the animal-based, low-carbohydrate diet did not result in weight gain despite the high fat content, ”said Hall.
These findings suggest that the factors leading to overeating and weight gain are more complex than the amount of carbohydrates or fat in a person’s diet. For example, Hall’s lab last year showed that a diet high in ultra-processed foods led to overeating and weight gain compared to a minimally processed diet that was tailored for carbohydrates and fat.
The low-fat vegetable diet contained 10.3% fat and 75.2% carbohydrates, while the low-fat animal diet contained 10% carbohydrates and 75.8% fat. Both diets contained approximately 14% protein and corresponded to the total number of calories presented to the subjects, although the low-carbohydrate diet contained twice as many calories per gram of food than the low-fat diet. On the low-fat menu, dinner can consist of a baked sweet potato, chickpeas, broccoli and oranges, while a low-carb dinner can consist of beef stir-fry with cauliflower rice. The subjects could eat whatever and however much they chose from the meals they were given.
Interestingly, our findings suggest benefits for both diets, at least in the short term. While the low-fat, plant-based diet helps to reduce appetite, the cruelty-free, low-carb diet resulted in lower and more stable insulin and glucose levels, ”said Hall. “We don’t know yet whether these differences will persist in the long run.”
The researchers note that the study was not intended to make dietary recommendations for weight loss, and the results may have been different if participants were actively trying to lose weight. Furthermore, all meals were prepared and provided to participants in an inpatient setting, making results difficult to replicate outside of the lab, where factors such as food costs, food availability, and meal preparation restrictions can make dieting difficult. However, the tightly controlled clinical environment allowed for objective measurement of food intake and data accuracy.
“To help us achieve good nutrition, rigorous science is critical – and now of particular importance, in light of the COVID-19 pandemic as we strive to identify strategies to help us stay healthy said NIDDK director Griffin P. Rodgers, MD, “This study brings us closer to answering long-sought questions about how what we eat affects our health.”
The research was supported by the NIDDK Intramural Research Program. Additional NIH support came from the National Institute of Nursing Research under grant 1Z1ANR000035-01.
About the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK): The NIDDK, part of the National Institutes of Health (NIH), conducts and supports research on diabetes and other endocrine and metabolic diseases; digestive diseases, diet and obesity; and renal, urological and haematological diseases. These illnesses span the full spectrum of medicine and affect people of all ages and ethnicities, and include some of the most common, serious, and debilitating conditions that affect Americans. See http://www.niddk.nih.gov for more information about the NIDDK and its programs.
About the National Institutes of Health (NIH):
NIH, the national medical research agency, includes 27 institutes and centers and is part of the United States Department of Health and Human Services. NIH is the premier federal agency that conducts and supports basic, clinical, and translational medical research, investigating the causes, treatments, and cures for both common and rare diseases. To learn more about NIH and its programs, visit www.nih.gov.
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References
Hall KD, et al. Effect of a plant-based, low-fat diet versus an animal, ketogenic diet on ad libitum energy intake. Nature Medicine. January 21, 2021.