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Effect of Low-Carbohydrate Diets High in Either Fat or Protein on Thyroid Function, Plasma Insulin, Glucose, and Triglycerides in Healthy Young Adults

Ullrich, I.H., Peters, P.J., Albrink, M.J., "Effect of Low-Carbohydrate Diets High in Either Fat or Protein on Thyroid Function, Plasma Insulin, Glucose, and Triglycerides in Healthy Young Adults," Journal of the American College of Nutrition, 4(4), 1985, pages 451-459.

The following information was written by Atkins professionals.

The purpose of this study was to evaluate the effect of diet on thyroid function. Two liquid formula diets with the same number of calories, both low in carbohydrate, were given to seven healthy volunteers (six men, one woman), who were within their ideal weight range. Each diet was consumed for seven days. One diet was high in polyunsaturated fat, the other high in protein. Calories in both diets were sufficient to prevent weight loss. Both diets were free of cholesterol and saturated fat. The nutrient distribution of the high-fat diet was 55% calories as fat, 10% as protein and 35% as carbohydrate. The high-protein diet was 35% protein, 30% fat, and 35% carbohydrate. All subjects were initially given 3,000 calories per day, with modifications as needed to maintain body weight. Fasting blood samples were obtained at the beginning of the study and before and after each test period. Both groups lost small but significant amounts of weight (approximately 3 pounds) on both diets. After consuming the liquid meal, insulin response was significantly higher 30 minutes later and the glucose level lower 120 minutes later in the high-protein versus the high-fat group. Thyroid function did not change after either diet. TSH, the hormone responsible for regulating the release of thyroid hormone, decreased significantly after both diets. T3, a particular thyroid hormone, decreased more after the high-fat diet compared with the high-protein diet. Total cholesterol levels decreased after both diets. Triglycerides were lower following the high-fat diet compared to the high-protein diet. There was an insignificant decrease in HDL (“good”) cholesterol in both groups. The authors concluded that benefits of replacing carbohydrate with polyunsaturated fat rather than protein are lesser insulin response and a lower spike in blood glucose following a meal, as well as lower triglycerides.

The following information was written by Atkins professionals.

The findings of this study can be applied to the Atkins Principle of Disease Prevention. High-fat/high-protein diets are useful in regulating glucose and insulin levels, improving lipid profiles and aiding in weight loss. These are all positive adaptations that will reduce risk for many chronic diseases. Subjects in this study still lost weight even though the high-fat and high-protein diets were relatively high in carbohydrate (as much as 100 grams per day). A three-pound loss in one week is a significant weight loss for such a short period of time. High-fat/high protein diets had few negative effects on thyroid function. Although TSH and T3 decreased, it should be noted that these parameters would naturally decrease as a result of any diet that results in weight loss.