Obesity is increasing amongst adults and children in Western countries, and although it has been extensively studied the cause is not certain. Amongst adults in the US the prevalence of obesity was 11.9% in men and 16.6% in women, according to the National Health and Nutrition Examination Survey (NHANES) conducted in the US in 1971 to 1975. However the same survey conducted in 2003 to 2004 found that obesity prevalence had increased to 31.1% in men and 33.2% in women. Identifying trends in macronutrient consumpt0on and energy intakes is an effective way to assess associations with obesity. For example, studies have previously identified that whole grain consumption has fallen in the last century, while at the same time sugar consumption has increased. In addition, total energy intakes have increased as extensive farming practices improve the efficiency of manufacturing cheap, palatable foods.
Researchers1 have compared data from the NHANES study of 1971 to 1975 with the data from 2005 to 2006 to identify associations with the increase in obesity. The results showed that between 1971 and 2006, the percentage of energy derived from carbohydrates increase from 44.0% to 48.7% while the percentage of energy derived from fat decreased from 36.6% to 33.7%. The energy derived from protein remained fairly constant changing from 16.5% to 15.7%. When the total energy intake was assessed for normal weight (BMI 19 to <25 kg/m2), overweight (BMI 25 to <30 kg/m2) and obese individuals (BMI ≥30 kg/m2) it was found that energy had increased in all three groups. Interestingly for every 1% increase in energy derived from protein, there was a decrease in total emery intake of 23 kcal at the expense of carbohydrates, or 51 kcal at the expense of fat.
These results support other studies that show an association between increased protein intake and protection from obesity. Protein may be beneficial to weight loss because it delays gastric emptying, stimulates secretions of gustatory satiety hormones such as peptide YY, is expensive to metabolise compared with carbohydrate and fat, and is preferentially used for structural turnover rather than as a source of energy. Other studies have shown that between 1977 and 2001 consumption of sugars in the form of sucrose and high fructose corn-syrup have increased, mainly from the increased consumption of carbonated soft drinks. Mechanistically, sucrose and high fructose corn syrup are able to cause insulin resistance as demonstrated in both human and animal studies. The fact that dietary fat intake has decreased since 1971 suggests that this is not the cause of the epidemic of obesity now present in Western nations.
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