It was the Russian non-conformist (I like him already) Ilya Ilyich Mechnikov who popularised the idea that gut bacteria were integral to human health. Metchnikoff won the Nobel Prize in 1908 for his immunological work that elucidated the phagocytic mechanism by which white blood cells engulf pathogens. However it is perhaps his work on conditions within the colon for which he is best known in nutritional circles. One thing that Metchnikoff realised, was that an acidic environment was necessary to support the beneficial microorganisms that inhabit the colon, and that alkalinisation of their habitat lead to the growth of pathogenic strains of bacteria that cause putrefaction and disease. In this regard Metchnikoff recommended the use of yoghurt to maintain the normal function of the gut, something that has been evidenced extensively since his early ideas. Yoghurt is beneficial because it seeds the gut with bacteria such as Lactobacillus acidophilus, which are present in yoghurt and responsible for its effective curdling from milk.
In the colon, beneficial strains of bacteria such as Bacteroides, Bifidobacteria and Lactobacillus acidophilus ferment dietary fibre and in the process produce short chain fatty acids such as acetate, butyrate and propionate which maintain the low pH in the colon necessary for health. In particular an acidic milieu within the colon may favour particular beneficial strains of bacteria and significantly alter the profiles of colonising microorganisms. High quality plant based diets containing polysaccharide fibres such as fructooligosaccharides (FOS) have been shown to provide nutrition that favours only beneficial Gram positive bacteria, and these beneficial strains may then outcompete pathogenic strains such as the Gram negative Salmonella or Escherichia coli. The short chain fatty acids produce by colonic bacteria are absorbed by the host organisms where they undergo metabolism in the liver. It is here that they are believed to be able to alter lipoprotein metabolism favourably, thus having a cholesterol lowering effect.
Researchers have known about the cholesterol lowering properties of consuming yoghurt for some time. For example, a paper published in 1979 in the American Journal of Clinical Nutrition1 investigated the effects of yoghurt on the cholesterol levels of healthy subjects. After just one week of supplementation of the subjects normal diet with yoghurt, there was a significant reduction in the total serum cholesterol levels from 202 to 191, mg/dL. When the subjects ceased consuming the yoghurt for three weeks serum cholesterol began to rise again, reaching 207 mg/dL, but fell back down to 189 mg/dL on recommencing yoghurt supplementation. In another study, the same researchers supplemented milk, pasteurised yoghurt or non pasteurised yoghurt to healthy subjects and found that all three treatments caused reductions in total plasma cholesterol concentrations compared to baseline levels. Analysis of the diets of the subjects showed that in most cases energy consumption increased.
Dr Robert Barrington’s Nutritional Recommendation: This study is interesting for two reasons. Firstly, cholesterol containing foods (yoghurt and milk) caused a reduction in plasma cholesterol levels. This adds more evidence to support the contention that the cholesterol theory of cardiovascular disease is seriously flawed. If dietary cholesterol is really able to cause elevation in plasma cholesterol, why did the cholesterol levels of the subjects decrease? Seconfly, the subjects gained no weight despite consuming an increased amount of calories. This adds more evidence to support the contention that energy intake is not the driver of weight gain some proponents claim. If additional energy intakes are able to cause weight gain, why did the subjects not gain weight? In this study yoghurt was more effective at causing reductions in cholesterol levels compared to milk. This may be due to the ability of yoghurt to provide beneficial bacteria and increase the production of short chain fatty acids. The milk may have cause reductions in cholesterol levels simply because the group consuming milk lost weight.
RdB
