If I were to summarise what is conventionally regarded as a ‘healthy’ diet, I’d say it would be one which is low in fat, and rich in carbohydrate, including fruit and vegetables and fibre. I don’t particularly have much enthusiasm for such as diet myself: while I’m a general fan of fruit of veg, I don’t subscribe to the low-fat/high-carb paradigm that is at the core of conventional dietary recommendations. Why? Well, it’s got something to do with the fact that there really isn’t very much evidence that such an approach brings broad benefits for health. That’s why.
I was interested to read a study published in the latest edition of the European Journal of Clinical Nutrition which assessed the effect of a traditionally ‘healthy’ diet in a group of 750 adults aged 35 or over. Some of the group were assigned to the ‘healthy’ diet (which included instructions to consume no more that 20 per cent of their calories in the form of fat), and some weren’t. The study lasted for 4 years.
A number of measurements were made including blood sugar levels, insulin levels, and the levels of substances known as insulin-like growth-factors (IGFs). Generally speaking, low levels of sugar and insulin would suggest a lower risk of diabetes. And lower levels of IGFs would suggest a reduced risk of cancer.
During the study, the intervention group reported eating half as much fat and twice as much fibre, fruit and vegetables as their counterparts. Now, some misreporting may have gone on here. But as the authors themselves admit, even taking this into account the likelihood was that the diet of the intervention group was significantly different (supposedly ‘better’) than the diet eaten by those left to do their own thing.
And now to the results�
Compared to the non-intervention group, those eating the ‘healthy diet saw:
No significant reduction in insulin levels
No significant reduction in IGF levels
And in those with a body mass index of 25 or more, there was no significant reduction in glucose (blood sugar) levels either
In fact, the only benefit to be found was a statistically significant reduction in blood sugar levels in individuals with a BMI of less than 25.
But before we get too excited about this, let’s just see how big this reduction was. Usually, levels of glucose in the bloodstream will vary between about 4.0 and 6.0 mmol/litre of blood (mmol/L). The average decline in glucose levels in individuals eating the ‘healthy’ diet with a BMI of less than 25 was about 0.03 mmol/L. I calculate that to be a reduction in blood sugar levels of less than 1 per cent: not exactly what you’d call Earth-shattering.
Let’s not beat around the bush: this study seems to be just another example of the ineffectiveness of conventional ‘healthy’ eating. There is now plenty of evidence that the low-fat/high-carb paradigm does not deliver on its promises. One wonders what it will take for health professionals and politicians who promote this brand of eating to start reading the research and taking heed of it.
Flood A, et al.The effects of a high-fruit and -vegetable, high-fiber, low-fat dietary intervention on serum concentrations of insulin, glucose, IGF-I and IGFBP-3. European Journal of Clinical Nutrition 2008;62:186″196