Humans can maintain body weight over long periods despite fluctuations in daily energy intakes, with regulation occurring via feedback mechanisms that take into account factors such as the weight and volume of the food. Most importantly, regulation occurs through feedback based on the energy density of the food. High density foods contain large amounts of energy for their weight and tend to be high in fat. In contrast, low density foods contain fewer calories because they have high water and fibre contents. Manipulation of the energy density of the food consumed in the diet can influence the short-term energy intake, but it is thought that longer-term energy intakes are not affected in the same way. Eating high density foods can therefore increase daily or weekly energy intakes, but over longer periods satiety reduces portion sizes to regulate energy balance.
For example, research1 has investigated the role of the energy density of food on calorie intake by examining 7 day food diaries from 371 men and 581 women. The diaries were analysed for relationships between the energy density of food, body size, total meal energy, as well as daily and weekly dietary energy intakes. All subject followed a free-living eating plan for 7 days. The results showed that higher density foods were associated with higher total energy intakes and comprised mainly of high fat foods. A high energy density of food was also associated with a higher rate of food intake as well as larger meal size. Energy density was not associated with body size, body mass index or weight, and this supports evidence from previous studies on twins that shows that differing the energy density of food does not affect body size.
High density foods tend to be high in fat, because fat contains over twice the energy of either protein and carbohydrate. However, the lack of association between the energy density of the food and the body weight, body size or body mass suggests that eating higher energy food does not cause long-term weight gain due to regulatory feedback mechanisms on satiety. Hormonal regulation of energy intake is complex and not fully understood, but it is known that leptin acts as a long-term feedback signal to the hypothalamus where it causes the release of pro‑opiomelanocortin and adrenocorticotropin hormone which suppresses the feeding urge. The lack of correlation between eating energy dense food and body weight, BMI or body size, suggest that weight gain and obesity is not simply caused by ad libitum over eating of high fat foods.
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