Читать книгу Clinical Obesity in Adults and Children - Группа авторов - Страница 113

Several lines of evidence, spanning global patterns of macronutrient intake distributions, experimental trials, and mechanistic studies, indicate that humans have the capacity to regulate the intake of macronutrients to an intake target as do other species.

Lieberman et al. [40] analyzed dietary macronutrient distributions from national survey data, including the US National Health and Nutrition Examination Survey (NHANES), and data from 13 countries with gross domestic products above $10,000 per capita per annum. The proportion of protein in the diets of all 14 countries was highly consistent at 16% of total energy, whereas calories from fat and carbohydrates were substantially more variable within and between populations. In the United States, protein, fat, and carbohydrate comprised 16, 33, and 48% of total energy intake, respectively.

Fat and carbohydrate varied significantly with age and race, but protein intake was not significantly related to demographic or lifestyle factors. These results support previous reports [e.g. 13,41] showing consistency across countries, populations, and time (Fig. 6.4a) of protein intake at ~15% of total energy, whereas fat and carbohydrate distributions vary more widely. Such consistency for protein is suggestive of regulation of the ratio of protein to non‐protein energy (fats and carbohydrates) in the diet.

Experimental studies have provided evidence for balancing macronutrient intakes in human subjects, with protein intake being especially closely regulated [e.g. 42–44]. Campbell et al. [45] allowed 63 subjects to freely compose a diet from foods containing 10, 15, and 25% protein for 3 days (Fig. 6.4b). Subjects closely tracked a mean 14.7% protein intake, which differed highly statistically significantly from the null expectation of no selection (16.7%). It is significant that the target intakes suggested by population studies and experimental studies converge within a narrow margin of 15–17%. Interestingly, this is not dissimilar for non‐human apes studied in the wild, which range between 10% (orangutan) and 20% (mountain gorilla), with our closest living relative, the chimpanzee, selecting a diet of 13% protein [35].

At a physiological level, there have been significant advances in understanding the mechanisms controlling macronutrient appetites [46]. Most notable has been the discovery that fibroblast growth factor (FGF)‐21 is the circulating signal of low‐protein status in humans and rodents. FGF‐21 is produced mainly in the liver and acts in the brain to stimulate protein appetite, guiding mice either to select protein‐rich foods if available or to increase intake of low‐protein diets to ensure increased protein intake, with associated increased energy intake on low‐protein, high‐energy diets [47,48]. FGF‐21 is also implicated in the inhibition of carbohydrate intake under low‐protein, high‐carbohydrate feeding in mice and humans [49–52].