Protein, Fat, and Carbohydrate Intake: Which Is the Most Stable?

The ideal breakdown of protein, fat, and carbohydrate intake remains largely debated, resulting in many adults modifying their macronutrient intake range based on what they believe is most optimal for their health. Diets that recommend varying macronutrient intake ratios have gained momentum, including low carbohydrate, high protein/low grain, and high fat/low carbohydrate diets, although evidence pointing to their benefits remains scarce and long-term success remains unclear largely due to non-compliance. A study compared the consistency of intake ranges for each of the macronutrients and found that protein intake was overall the most stable.

The National Health and Nutrition Examination Survey (NHANES; 2009-2014) was used to provide data on macronutrient intake as a percentage of total energy intake in the United States for 15,774 adults aged 19 years and older, with the exception of pregnant or lactating women. The difference between the 75th and 25th percentile interquartile ratios (IQRs) of macronutrient intake distributions was used to estimate variability in macronutrient intake. Additional intake data were collected from Australia, Canada, Czech Republic, Finland, France, Germany, Ireland, Japan, Korea, Netherlands, Norway, Poland, and the United Kingdom.

Per the NHANES data, among U.S. adults, macronutrient intake was: protein, 15.7% kcal; carbohydrate, 48.1% kcal; and fat, 32.9% kcal. The IQR of protein intake distribution was 3.73% kcal—41% of carbohydrate intake distribution (9.18% kcal) and 58% of fat intake distribution (6.4% kcal). Carbohydrate and fat IQRs varied largely by age and race, but protein intake IQR showed no relationship with sex, race, income, physical activity, or body weight. International mean protein intake was similar to that of the United States (16.3% kcal) and showed the least variance among the three macronutrients.

“A better understanding of the biological constraints on protein ingestion may improve formulation of practical guidance regarding optimal macronutrient intake,” the researchers concluded.