The fact that our collective mass has grown considerably of late has inevitably triggered warnings from health professionals about how this may swell our risk of weight-related conditions such as heart disease. Ideal weight recommendations traditionally come in the form of the body mass index (BMI) - calculated by dividing an individual's weight in kilograms by the square of their height in metres. However, the usefulness of the BMI in judging heart disease risk has recently been called into question in a study in The Lancet, which found that, once factors such as smoking and exercise habits were taken into consideration, the BMI has no significant bearing on heart-attack risk.
This study is not the only research that has cast some doubt on the relevance of the BMI as a predictor of our propensity to disease and death. Earlier this year, the journal Circulation published a study that found that in individuals having surgery for heart disease (coronary artery bypass), mortality after surgery was lowest in individuals whose weight was categorised as overweight (BMI of 25 to less than 30) or 'high-normal'. These results and those of the recent Lancet study clearly cast doubt on the appropriateness of standard medical recommendations that a 'healthy' BMI of between 19 and 25 is ideal in terms of heart health.
While research that asks questions of the conventional wisdom regarding the relationship between BMI and heart health is interesting, it is perhaps not as telling as research which seeks to establish the relationship between this measure of body weight and overall risk of death. Earlier this year, The Journal of the American Medical Association published a study stating that underweight and obesity (a BMI of 30 or more) were both associated with an increased risk of death. However, surprisingly, this study found that compared to those in the 'healthy' BMI category, those categorised as 'overweight' (a BMI of 25 to 29.9)were actually at reduced risk of death.
There is a growing recognition that it is not fat per se, but fat which aggregates around the middle of the body ('abdominal fat') that is strongly linked with health issues such as heart disease. The Lancet study found that a higher ratio of waist circumference to hip circumference (waist-to-hip ratio) was very clearly associated with increased heart attack risk. Ideally, men and women should have waist-to-hip ratios no larger than about 0.90 and 0.83 respectively. From a health perspective, the evidence suggests it is an individual's waistto-hip ratio, rather than their BMI, that represents their vital statistic.
Earlier this year, I wrote a column which focused on the evidence that protein has superior appetite-suppressing effects compared to the other major dietary constituents (carbohydrate and fat). This month saw the publication of a study in the journal Cell Metabolism, which sought to explore the basis for this finding. One factor which is believed to affect appetite is the level of sugar (glucose) in the vein which takes blood from the gut to the liver (the hepatic portal vein): higher glucose levels here have the ability to reduce appetite and food intake.
In the recent research, researchers in France found that feeding rats a protein-rich meal led to an increase in glucose levels in the hepatic portal vein by stimulating the production of sugar within the gut. These higher glucose levels also seemed to stimulate areas in the brain that play a role in appetite control. Interestingly, feeding rats a starch-rich diet led to smaller increases in glucose levels in the hepatic portal vein compared to those induced by protein.
The results of this study suggest that one of the ways protein may help reduce food intake is by stimulating the production of glucose in the gut, which in turn helps to quell appetite.
In a recent column you recommended omega-3 fish oils for brain health. But you didn't mention linseed as a suitable omega-3 source. Steve
In the column to which you refer I highlighted the evidence which suggests that a particular type of omega-3 fat known as eicosapentaenoic acid (EPA) is important for the day-to-day running of the brain, and may help to prevent or even alleviate psychological conditions, such as depression and schizophrenia. The richest natural source of EPA is fish oil (as found in oily fish or as fish-oil supplements). You are correct in stating that linseeds (flaxseeds) are rich in omega-3 fats. However, linseeds do not contain either EPA or DHA, but an omega-3 fat by the name of alphalinolenic acid. Evidence suggests that, within the body, ALA may be converted into EPA, but that this conversion is generally very limited in extent. The scientific work regarding mental health and omega3 fats has focused on EPA, and we simply don't know how beneficial ALA (from linseed oil or any other source) is likely to be for the brain.
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