In healthy young adults, eating either a high-fat diet or a high-protein low-carbohydrate diet for 7 days lowers thyroid-stimulating hormone (TSH) levels by a similar amount, suggesting that the type of macronutrient—fat or protein—does not determine the degree of TSH reduction.

When healthy young adults eat a low-carbohydrate diet with mostly polyunsaturated fat for seven days, their fasting T3 hormone levels drop compared to when they eat a low-carbohydrate diet with higher protein content.

Among adults aged 18 to 45, thyroid hormone levels were within normal range at the start of the study, so changes in micronutrient levels during the 60-day intervention were not influenced by thyroid issues.