I would generally advise anyone wishing to avoid developing diabetes to keep their diet relatively low in foods that tend to cause considerable disruption to blood sugar levels. These would include many starchy carbohydrates including most forms of bread, potato, rice, pasta and breakfast cereals. It would also include foods that contain added sugar. Eating less of these sorts of foods will tend to reduce the amount of insulin secreted by the pancreas. This, in time, should reduce the risk of the pancreas exhausting (leading to inadequate levels of insulin) or the effect of insulin becoming somewhat nullified (a situation known as ‘insulin resistance’). Inadequate insulin and/or insulin sensitivity are the key underlying factors in type 2 diabetes.
There is some so-called ‘epidemiological’ evidence linking the consumption of high glycaemic index(fast sugar releasing foods) and an increased risk of type 2 diabetes. However, such studies can only really tell us about associations between things, and cannot be used to conclude cause and effect. In other words, while epidemiological studies may find an association between high glycaemic index (GI) food intake and enhanced risk of type 2 diabetes, we do not know whether the high GI foods are doing the damage here. It might be, for instance, that individuals who eat lots of high GI foods also tend to be very sedentary, and it’s the lack of activity (not the high GI foods) that is causing them to be at increased risk of diabetes.
Cause and effect is much better discerned through ‘intervention’ studies, where individuals are, say, required to change their diets to see what effect this has on their health or markers of health. Such as study, concerning diet and diabetes, was recently published in the Archives of Pediatric and Adolescent Medicine . 54 adolescents (average age 15) were randomised to one of three groups:
1. a diet lower in sugar and higher in fibre
2. a diet lower in sugar and higher in fibre plus strength training
3. no intervention (control group)
The study lasted for 16 weeks.
At the end of the study, about half of all the participants (there was available data 49 individuals) on had managed to reduce their sugar consumption. The average reduction in consumption in these individuals was 47 g per day (the amount of sugar found in about one can of sweetened soft drink).
Individuals were tested at the start and end of the study with glucose tolerance tests. Here, sugar was ingested or injected into the individuals, and sugar and insulin levels monitored for some time after. Overall, individuals who had reduced their sugar intake saw an average of 15 per cent drop in sugar levels and 33 per cent drop in insulin levels on testing. These results (both statistically significant) are consistent with the idea that those who consumed less sugar would be at significantly reduced risk of type 2 diabetes.
In this study, 59 per cent of individuals managed to eat more fibre. In these individuals, average increase was 5 grams per of fibre per day. These individuals saw a statistically significant reduction in their body mass index of 2 per cent. Personally, I think the body mass index is pretty useless as a marker for health, because it tells us nothing about body composition. However, in this study, individuals also had the levels of ‘visceral adipose tissue’ checked with MRI scanning. Visceral adipose tissue is fat that aggregates around the internal organs, and is associated with an increased risk of chronic disease including heart disease and type 2 diabetes. Those who had managed to increased their fibre intake say a fall in visceral adipose tissue of 10 per cent.
The authors of this study concluded that: “Individuals who reduced added sugar intake by the equivalent of 1 can of soda per day or increased fiber intake by the equivalent of a cup of beans showed improvements in key risk factors for type 2 diabetes, specifically in insulin secretion and visceral fat.”
I think it’s worth point out that while there were 3 intervention groups, the dietary changes were similar in all three groups. In other words, the control group also reduced their sugar consumption and increased their fibre intake to an extent similar to those who had been asked to make these changes. Ultimately, what the authors of this study analysed was the effect of dietary change, not the effect of the dietary advice to reduce sugar and increase fibre intake. This is a key point, which was touched on in a recent blog post here.
Ventura E, et al. Reduction in risk factors for type 2 diabetes mellitus in response to a low-sugar, high-fiber dietary intervention in overweight Latino adolescents. Arch Pediatr Adolesc Med. 2009;163(4):320-7.