Dietary factors that decrease the risk of type 2 diabetes

Last week we discussed the effects that certain foods have on the risk of type 2 diabetes mellitus (T2 DM). High protein intakes were found to increase the risk of T2 DM by up to 67%, while a high dietary fibre intake of about 35 g per day reduced T2 DM by 34%. These findings are based on meta-analyses of results obtained with multiple investigations and very large combined study populations.

In this article we will look at some of the other dietary factors that may play a role in lowering the risk of developing T2 DM, as reported in the insightful lecture Dietary Factors for the Prevention of Diabetes Mellitus presented by Prof Renée Blaauw at SASA’s “Nutrition in NCD Prevention Roadshow” held in Pretoria earlier this year.

Dairy products

Milk and dairy products such as yoghurt, cheese and amazi/maas are often blamed for a variety of ills, and many people have told me that they are cutting out dairy to improve their health! Where this erroneous attitude comes from is a mystery as dairy products contain the highest quantity of easily absorbable and utilisable calcium in the human diet.

Read: Dairy diary: the lowdown and the heads-up

The meta-analysis of 7 studies that probed the effect of dairy products on the risk of developing T2 DM, showed that individuals who had the highest intake of milk and dairy products were 14% less likely to develop T2 DM compared to people who consumed very little dairy.

Further analysis of the data obtained with the combined studies, identified a difference in effect depending on the fat-content of the dairy products that were studied. The total positive effect of dairy products produced a reduction in risk of 14% as mentioned above, but low-fat dairy products (low-fat milk, yoghurt, amazi, cottage cheese) reduced the risk by up to 18%. In general, risk of T2 DM was lowered by 10% for every extra serving of low-fat dairy per day.

Gao and co-authors, concluded from their study that “a modest increase in daily intake of dairy products such as low fat dairy, cheese and yoghurt may contribute to the prevention of T2 DM”. They caution that these results need to be confirmed with randomised controlled trials.

Tong and his team suggest that calcium, vitamin D and whey proteins in dairy products may help to reduce the risk of T2 DM. For example, there is some evidence that whey proteins can increase insulin sensitivity.

Omega-3 Fatty Acids

One would expect protective compounds such as omega-3 FAs, to be useful in preventing T2 DM, but a meta-analysis conducted by Wu and co-authors at the Harvard School of Public Health, Boston, USA, was not able to identify either a negative or a positive effect of fish consumption (fish/seafood are rich sources of omega-3 FAs) on T2 DM. The basic results of the meta-analysis appeared to be neutral. However, the results did show that alpha-linolenic acid (ALA), an omega-3 FA derived from plants which is found in linseed and flax oils, may possibly slightly lower the risk of T2 DM.

Read: Omegas explained

Considering that T2 DM is associated with chronic, low-grade inflammation, particularly in fat tissue and that signals from the chronically inflamed tissue prevent insulin from working efficiently, it is feasible to expect that anti-inflammatory compounds like omega-3 FAs would counteract inflammation and thus help to reduce the risk of T2 DM. More in-depth research may help to clarify the role of omega-3 FAs and fish/seafood/omega-3-rich plants as sources of EPA, DHA and ALA (omega-3 FAs) in reducing the risk of T2 DM.

The Coffee Saga

Coffee has been blamed for years as a cause of a variety of human conditions including insulin-dependent diabetes and T2 DM. More recently however, research has begun to exonerate this maligned beverage! Much more positive findings have emerged about coffee lately and this also applies to the role that coffee may play in the development of T2 DM.

Researchers at Harvard University combined the results of more than 1,1 million study participants, including 45,335 people with T2 DM, to determine if caffeinated coffee or decaffeinated coffee increases or decreases the risk of this disease.

Read: Coffee? Go for it!

Coffee consumption was found to be inversely associated with the risk of T2 DM, which means that the more coffee the subjects consumed, the lower their risk of developing T2 DM. This was true for both caffeinated and decaffeinated coffee. One cup of coffee a day reduced the risk of T2 DM by 8% and 6 cups of coffee per day reduced the risk by 23%. It is important to keep in mind that none of the studies determined what effect adding milk or sugar to coffee may have on coffee’s protective effect.

The authors of this study suggest that compounds such as chlorogenic acid, a phenolic compound found in coffee, may be responsible for the positive effect, because chlorogenic acid reduced blood glucose concentrations in studies using experimental animals. Other bioactive components of coffee like lignans, quinides and trigonelline may also be implicated.

Because it appears that the protective effect exerted by coffee on the risk of T2 DM is not linked to its caffeine content, it is prudent not to consume more than 6 cups of caffeinated coffee a day. Increasing caffeine intake may cause a variety of other physiological effects, which are not positive, including increased heart rate or palpitations, increased blood pressure, insomnia, tremors and jitteriness, to name but a few. The recommendation is, therefore, to consume coffee in moderate quantities of not more than 6 cups a day. Both caffeinated and decaffeinated coffee can apparently protect us against the risk of developing T2 DM.

Conclusions

Thanks to the excellent lecture present by Prof Blaauw and the meta-analyses conducted by the various researchers mentioned in her talk, our understanding of dietary factors that can reduce the risk of T2 DM has expanded to include low-fat dairy products and moderate quantities of caffeinated or decaffeinated coffee.

Omega-3 FAs as found in fatty fish or seafood, did not have a significant protective effect against Type 2 diabetes mellitus, but this finding should not detract from the other protective roles played by omega-3 FAs in cardiovascular disease and other inflammatory conditions.

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