December 9, 2014

expert reaction to increased BMI and cardiometabolic risk markers

Researchers publishing in the journal PLOS Medicine have studied metabolic markers and changes in weight, reporting variations in these markers with changes in weight, fat level, and BMI.

Prof. Tom Sanders, Professor emeritus of Nutrition and Dietetics, King’s College London, said:

“The limitation of this study is that it uses surrogate risk markers of disease rather than disease outcomes. BMI also reflects differences in muscle mass as well as fat with people of African origin having higher BMI owing to more muscle than those of European origin. Waist circumference is probably a better index of risk of type 2 diabetes with people with a BMI <30 kg/m2 for the men it should not exceed 94 cm and for women 80 cm (about 37 and 32 inches respectively).

“The relationship between BMI and mortality is J-shaped with both high a low BMI being associated with increased risk. While increasing BMI is associated with greater risk of type 2 diabetes and cardiovascular disease, low BMI is associated with an increased risk of death particularly from lung and infectious diseases. Ideally, adults should maintain the weight attained in early adult life and be weight stable and this helps reduces some of the increase blood pressure and cholesterol that occur with age. Some weight gain, say an increase of 2 kg/m2, is typical as most adults approach middle-age but the hazards associated with this are modest compared with cigarette smoking, especially for women. However, it is a bad message for young people to suggest lower BMI values than those currently accepted are better given the scale of eating disorders in young people.”

Prof. Keith Frayn, Emeritus Professor of Human Metabolism, University of Oxford, said:

“There has been much debate about whether overweight (usually taken as a Body Mass Index from 25 to 30 kg/m2), as opposed to frank obesity, poses health hazards. Some large-scale data from the Centers for Disease Control and Prevention in the U.S. (JAMA 2005) suggest not. But the results of this study suggest that, indeed, there are adverse changes in blood markers with increasing degrees of overweight.

“Interestingly, these results in young adults give no evidence for the U-shaped relationship often observed between BMI and mortality – i.e. other data suggest that there is an optimum BMI which is neither too thin nor too fat. The data in this paper support a continuous worsening of metabolic state with increasing fatness. It is well recognised that the U-shaped relationship can reflect confounding by smoking (smokers tend to be lean and unhealthy) and by inclusion of people who are thin because they are already ill; but even when these confounders are eliminated so far as practicable, the U-shape is usually still seen (the Prospective Studies Collaboration, Lancet 2009, found an optimum BMI of 22·5–25 kg/m² after elimination of these confounders so far as was possible: mortality was greater in people below and above this range).

“The use of Mendelian Randomization in the present study adds support to the interpretation that the adverse blood changes are a direct result of increasing adiposity, and the paper confirms very positive effects of weight loss. However, it must be noted that the results in this paper are based on blood measurements, and not on actual mortality.  Whilst there are good reasons for believing that some of the changes found in blood markers would be associated with increased disease or mortality, other blood markers measured in this paper have an unknown or uncertain relevance to health.

“The results add further emphasis to the need to limit fat accumulation in early adulthood, and confirm the widespread metabolic benefits of weight loss.”

Prof. Nick Finer, Consultant Endocrinologist and Bariatric Physician, University College London Hospitals, said:

“This important and rigorous study of young Finns confirms that even within accepted ‘healthy’ Body Mass Index (BMI) range, young adults have increasing markers of cardiovascular risk such as elevated lipids, measures of inflammation, disordered liver function and insulin resistance with increasing weight. This confirms previous data in adults that it is better to have a BMI at the lower end of the so-called normal range of 18.5- 25 kg/m2. By using the technique of ‘Mendelian Randomisation’ whereby subjects are separated for comparison by the genes that risk obesity rather than the subjects measured BMI, the study goes much further in showing that the increasing weight is the cause of these abnormalities not just an association. Furthermore they have shown that increases or decreases in weight over a six-year period respectively exacerbate or improve these risks.

“This study acts as a further warning about the perils of even modest degrees of overweight on the future health of young people. Other research has shown that actual end-organ damage (for example furring-up of arteries) takes longer to develop, so the potential benefits from both prevention, and weight loss on later developing cardiovascular disease such as stroke and heart attack, adds to the need for tackling excess weight as a public health priority.”

‘Metabolic signatures of adiposity in young adults: Mendelian randomization analysis and effects of weight change’ by Würtz et al. published in PLOS Medicine on Tuesday 9th December. 

Declared interests

None declared