Increasingly it is being evidenced that low quality foods are the cause of weight gain. High quality foods can be eaten ad libitum without changes in body weight, but lower quality foods do not share this property. When low quality foods are consumed, normal energy and appetite regulatory mechanisms become disrupted, insulin resistance develops, oxidative stress and inflammation become systematic, and these changes are associated with weight gain. The driver of obesity is likely the development of insulin resistance, and insulin resistance in turn has been shown to be caused directly by consumption of low quality foods, particularly those containing fructose, trans fats and oxidised fats. These food components are metabolic poisons, and may damage normal metabolic regulation. Fructose for example increases de novo lipogenesis rates in the liver, over supplying fatty acids to the circulation, leading to insulin resistance. Oxidised fat and trans fat increase oxidative stress, and this may also induce insulin resistance.
The biochemical effects of individual food components can be measured in the laboratory using a number of cell culture, animals and human clinical tests. However, it is not so easy to assess the effects of whole foods in real life situations. Despite the difficulties researchers have attempted to assess the long term effects of whole foods, and for this purpose one of the best techniques is to measure associations between particular food groups and weight changes in free living individuals over a long time period. For example, one such study1measured the weight changes in over 120,000 individuals over 4 year periods from between 1986 and to 2006 and then estimated the food intakes of these individuals. From this body weight changes were calculated and the data examined for correlations between these body weight changes and consumption of particular food groups. This allowed the authors of the paper to group a number of foods into high quality weight loss foods and low quality weight gain foods.
The results of this study showed that in each 4 year period, intakes of crisps (potato chips), potatoes, sugar sweetened soft drinks, unprocessed red meat and processed red meats were associated with increases in weight of 1.69, 1.28, 1.00, 0.95 and 0.93 lbs, respectively. In contrast, in each 4 year period, intakes of vegetables, whole grains, fruits, nuts and yoghurt were associated with weight loss of 0.22, 0.37, 0.49, 0.57 and 0.82 lbs, respectively. The association between potatoes and weight gain is likely a reflection of the fact that potatoes are frequently used to make low quality foods, and are often refined by removing their skins. Unprocessed red meat is also not inherently of low quality, but generally people eat too much low quality red meat from non-organic grain fed sources. Such meat is high in omega-6 fats and this may explain the association with weight gain. Excluding potatoes and red meat, there should be no surprises that the other foods are associated with the weight changes reported based on previous data.
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