In the Battle Between Two Eating Patterns, Both Win

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When it comes to diabetes, lower calorie intake may not be the only factor in determining blood sugar and insulin levels.

A small study at the NIH done by scientists at the National Institute of Digestive and Kidney Diseases looked at the impact of two diets on caloric intake, levels of hormones, body weight and more. Those on a low-fat, plant-based diet may have eaten less, but experienced higher insulin and blood sugar levels when compared to subjects that ate a low-carb, animal-based diet. 

The initial thinking was that high-fat foods would lead to higher calorie intake given the calorie density per gram. However, high-carb foods may cause big changes in blood sugar and insulin that could promote increased appetite and consequently, overeating according to Keven Hall, PhD, the lead author of the study. His study was used to evaluate if high-carb or high-fat diets lead to increased energy intake. 

In this study, 20 non-diabetic adults were housed for 4 consecutive weeks in the Clinical Center’s Metabolic Clinical Research Unity of the NIH. Of the subjects, 11 were men and 9 were women. Each received a plant-based, low-fat diet or animal-based, low-carb diet for two weeks then switched after two weeks to the other diet. Neither diet contained highly-processed foods and had equal amounts of non-starchy vegetables. The low-carbohydrate diet was high in fat while the low-fat diet contained higher amounts of carbohydrates. Three meals and snacks were provided to the subjects and they were allowed to eat as much as they liked.

People in the low-fat diet ate between 500 and 700 less calories per day compared to when they consumed the low-carb diet. However, subjects didn’t report any differences in hunger, pleasure in meals, or satiety between the two diets. Subjects reduced their weight on both diets, but the low-fat diet had a more significant loss of body fat. 

The higher glycemic index carbohydrates consumed produced more profound blood sugar and insulin swings, but calorie intake was less and loss of body fat was higher. This challenges the idea that high-carb diets make people overeat. However, animal-based, high-fat diets didn’t lead to weight gain, even when higher in fat and calories, stated Hall.

The results indicate that factors leading to overeating and weight gain are more complicated than the amount of carbohydrates or fat in an individuals’ diet. Hall’s studies previously found that an ultra-processed diet was linked with overeating and weight gain compared to a minimally-processed diet with the same amounts of carbs and fat. 

The plant-based, low-fat diet was roughly 10% fat and 75% carbohydrate and the animal-based diet was the opposite: 10% carbohydrate and roughly 75% fat. Each diet provided about 14% protein and had a similar calorie level presented to the participants, but the low-carb diet had double the calories per gram of food than the low-fat diet. An example for dinner on the low-fat menu would be a baked sweet potato, chickpeas, broccoli, and oranges while the low-carb dinner might be beef stir fry with rice made of cauliflower. Participants were allowed to eat as much as they wanted of the meals provided. 

In the short term, benefits were observed for both diets. While the plant-based, low-fat diet helped curb appetite, the low-carb, animal-based diet led to lower and more stable insulin and blood sugar levels. It’s unclear if these differences would be maintained over time. 

This study wasn’t developed to provide diet recommendations for weight loss, according to the researchers, and findings could have been different if subject were trying to lose weight on purpose. Results could have also been different had the subjects been on their own to make their own meals versus having meals prepared in a more tightly-controlled environment. 

The researchers note that in the age of COVID, discovering how diet impacts health is quite important to staying healthy. Dietitians can advise a mix of both types of diets for good health:

  • Choose whole grains over processed grains and limit the number of servings.
  • Include green leafy vegetables at meals, given their low-carbohydrate content.
  • Choose low-fat varieties of dairy products such as skim or 1% milk or low-fat yogurt.
  • Include lean sources of protein at meals such as fish, skinless poultry, and lean cuts of beef.
  • Include healthy fats for satiety including avocado, olives, ground flaxseed, nuts, and seeds.
  • Add a variety of fruits with meals.
  • Include meat-less meals that include beans, lentils, or soy-based products.
  • Add seafood to your diet a few times per week for heart health.
  • Cut empty calories from sugar, alcohol, and processed snacks from your diet.
  • Stay active! Exercise boosts immunity, aids in weight management, and furthers chronic disease reduction.

By Lisa Andrews, MEd, RD, LD


  1. Kevin D. Hall, Juen Guo, Amber B. Courville, James Boring, Robert Brychta, Kong Y. Chen, Valerie Darcey, Ciaran G. Forde, Ahmed M. Gharib, Isabelle Gallagher, Rebecca Howard, Paule V. Joseph, Lauren Milley, Ronald Ouwerkerk, Klaudia Raisinger, Irene Rozga, Alex Schick, Michael Stagliano, Stephan Torres, Mary Walter, Peter Walter, Shanna Yang, Stephanie T. Chung. Effect of a plant-based, low-fat diet versus an animal-based, ketogenic diet on ad libitum energy intakeNature Medicine, 2021; DOI: 10.1038/s41591-020-01209-1
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