Traditionally, the carbohydrate content of the human diet contained unrefined sources of cereal grains. However, modern food manufacturing processes has increased the ease with which these natural foods can be refined. Modern Western diets how contain carbohydrates predominantly in their refined form, and the amount of unrefined whole grains has fallen. This is problematic because unrefined whole grains are a good source of minerals, fibre and vitamins. The rise in the consumption of refined carbohydrates, and concomitant decrease in consumption of whole grains has been suggested as one reason for the rise in the incidence of metabolic syndrome. Characterised by insulin resistance and abdominal obesity, the metabolic syndrome increases the risk for type 2 diabetes and cardiovascular disease. Evidence suggests that the re-introduction of whole grains to the diet can prevent or reverse the development of metabolic syndrome.
Research1 has investigated the effect of diet and exercise intervention on some of the risk factors for cardiovascular disease in 31 overweight individuals with metabolic syndrome. Of the subjects, 13 were diagnosed as having type 2 diabetes, 5 with cardiovascular disease, and the rest had >1 risk factor for metabolic syndrome. The subjects performed a 21 day diet and exercise regimen that allowed ad libitum eating, but specified that carbohydrates (65 to 70% of total energy) must be from unrefined whole grains, vegetables and fruits. The fat content of the diet was not to exceed 12 to 15% with emphasis on increasing the polyunsaturated to saturated ratio (2.4:1). Protein sources were from either fish, fowl or vegetable sources and made up 20% of the total energy content. Exercise consisted of walking for 45 to 60 minutes every day on a tread mill
Blood samples of the subjects were analysed to asses the serum lipids, glucose, insulin, oxidative stress and inflammation both pre- and post-intervention. Following the exercise and diet regimen, significant reductions in body weight and body mass index were seen in the subjects suggesting that fat loss had occurred. Serum lipids had also decreased and the lipid ratios showed favourable changes. In particular, decreases in total cholesterol, LDL-cholesterol, HDL-cholesterol, triglycerides, LDL to HDL ration and total cholesterol to HDL ratio. The plasma fasting glucose and insulin levels significantly decreased and estimates of insulin resistance suggested significant improvements in insulin receptor sensitivity. Decreases in oxidative stress were demonstrated by reductions in plasma myeloperoxidase and 8-isoprostaglandin F2α, and decreases in systemic inflammation were demonstrated by significant reductions in plasma C-reactive protein. Significant improvements were also seen in a number of other markers of cardiovascular disease.
This study demonstrates that dietary and exercise intervention are able to decrease risk factors associated with cardiovascular disease. This supports previous studies in this field and taken together, suggests that cardiovascular disease may be caused by lifestyle factors. Interestingly, previous studies have shown that subjects who improve their diet have equal benefit to those who also incorporate exercise into their lifestyle programmes. It would have therefore been interesting to compare the diet and exercise group with both a diet only, and exercise only group. Cardiovascular disease is increasingly being linked to inflammation, and this study demonstrates that lifestyle intervention is successful strategy in reducing systemic inflammation. Increasing the quality of the diet has been shown in many studies to decrease systemic inflammation, particularly diets based on unrefined plant foods such as the Mediterranean diet (here).
Another interesting aspect of this study was the choice to allow the subjects ad libitum energy intakes, only restricted by the types of food choices available. This provides further insight into the diet quality versus energy balance debate for weight loss. Generally, restricting energy intake alone can be successful at providing short-term weight loss, but questions remain regarding its benefits in long-term weight loss. Weight gain is complex, but metabolic abnormalities characterise its development. Therefore correction of the abnormalities by improvements in the quality of foods eaten may be essential to allow long term weight loss from ad libitum energy intakes. Plant foods high in dietary fibre, micronutrients and phytonutrients have been extensively researched for their health benefits and appear to show promise at reversing obesity, metabolic syndrome and cardiovascular disease, without the need for calorie restriction.
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