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We apply nutritional geometry, a framework for modelling the interactive effects of nutrients on animals, to help understand the role of modern environments in the obesity pandemic. Evidence suggests that humans regulate the intake of protein energy (PE) more strongly than non-protein energy (nPE), and consequently will over- and under-ingest nPE on diets with low or high PE, respectively. This pattern of macronutrient regulation has led to the protein leverage hypothesis, which proposes that the rise in obesity has been caused partly by a shift towards diets with reduced PE:nPE ratios relative to the set point for protein regulation. We discuss potential causes of this mismatch, including environmentally induced reductions in the protein density of the human diet and factors that might increase the regulatory set point for protein and hence exacerbate protein leverage. Economics--the high price of protein compared with fats and carbohydrates--is one factor that might contribute to the reduction of dietary protein concentrations. The possibility that rising atmospheric CO₂ levels could also play a role through reducing the PE:nPE ratios in plants and animals in the human food chain is discussed. Factors that reduce protein efficiency, for example by increasing the use of ingested amino acids in energy metabolism (hepatic gluconeogenesis), are highlighted as potential drivers of increased set points for protein regulation. We recommend that a similar approach is taken to understand the rise of obesity in other species, and identify some key gaps in the understanding of nutrient regulation in companion animals.

Objective: Obesity is a major risk factor for the development of type 2 diabetes. Tumor necrosis factor (TNF)-alpha is a candidate gene for the development of both obesity and insulin resistance. We investigated whether a common polymorphism in the promoter region (-308 G/A) of the TNF-alpha gene was associated with increased risk for the development of insulin resistance and cardiovascular disease in an obese Australian population., Research Methods and Procedures: Obese, non-diabetic subjects (146 women and 34 men) were genotyped with polymerase chain reaction-restriction fragment length polymorphism techniques, and anthropometric and biochemical measurements were analyzed. A homeostasis model assessment (HOMA) score was used to gauge the level of insulin resistance., Results: The frequencies of the G allele and the A allele were 0.759 and 0.241, respectively. Subjects homozygous for the A allele had higher fasting insulin levels (226 vs. 131 pM; p < 0.001), higher HOMA scores (10.2 vs. 5.3; p < 0.001), higher systolic blood pressure (143 vs. 129 mm Hg; p = 0.02), and lower high-density lipoprotein (HDL) cholesterol (1.13 vs. 1.25 mM; p = 0.04) than did subjects homozygous for the G allele. Whereas an association between insulin resistance and body mass index or waist circumference was seen in all subjects, a highly significant negative correlation of HDL cholesterol to HOMA scores (r = -0.710; p < 0.001) occurred in subjects with the A allele only., Discussion: The -308 G/A TNF-alpha gene variant conveys an increased risk for the development of insulin resistance in obese subjects. The presence of low HDL cholesterol levels further increases the risks associated with insulin resistance in carriers of the A allele.

A significant contributor to the rising rates of human obesity is an increase in energy intake. The 'protein leverage hypothesis' proposes that a dominant appetite for protein in conjunction with a decline in the ratio of protein to fat and carbohydrate in the diet drives excess energy intake and could therefore promote the development of obesity. Our aim was to test the 'protein leverage hypothesis' in lean humans by disguising the macronutrient composition of foods offered to subjects under ad libitum feeding conditions. Energy intakes and hunger ratings were measured for 22 lean subjects studied over three 4-day periods of in-house dietary manipulation. Subjects were restricted to fixed menus in random order comprising 28 foods designed to be similar in palatability, availability, variety and sensory quality and providing 10%, 15% or 25% energy as protein. Nutrient and energy intake was calculated as the product of the amount of each food eaten and its composition. Lowering the percent protein of the diet from 15% to 10% resulted in higher (+12±4.5%, p = 0.02) total energy intake, predominantly from savoury-flavoured foods available between meals. This increased energy intake was not sufficient to maintain protein intake constant, indicating that protein leverage is incomplete. Urinary urea on the 10% and 15% protein diets did not differ statistically, nor did they differ from habitual values prior to the study. In contrast, increasing protein from 15% to 25% did not alter energy intake. On the fourth day of the trial, however, there was a greater increase in the hunger score between 1-2 h after the 10% protein breakfast versus the 25% protein breakfast (1.6±0.4 vs 25%: 0.5±0.3, p = 0.005). In our study population a change in the nutritional environment that dilutes dietary protein with carbohydrate and fat promotes overconsumption, enhancing the risk for potential weight gain. [ABSTRACT FROM AUTHOR]

The author discusses the integration of nutrients, foods, diets, and appetites with obesity and cardiometabolic health. He says that the incidence of obesity and linked cardiometabolic diseases (OACD) has continued to increase amidst debates as to whether fat, simple carbohydrates, or energy by itself is to blame.