Does Extra Body Fat Help You Live Longer?

iDiet Co-Founder and Chief Scientific Advisor Susan Roberts, PhD shares her views on a new study being reported in the popular press this week. 

What’s the Story?

A study published in JAMA this week (Flegal et al. January 2, 2013) reported a meta analysis of 100 studies looking at the relationship between age of death and BMI.  A meta analysis is a formal summary that combines multiple studies on the same topic and helps give an overview of the research field.

The results of the study show that people who are overweight (BMI 25-30) do not in fact die earlier than normal-weight people. Even category 1 obese people (BMI 30-35) do not appear to die earlier — the study shows that premature death is restricted to people who have a BMI of over 35.

Does this mean that people should give up on trying to lose weight for health? Absolutely not, and here is why:

1. Categorization  This study lumped everyone with a BMI of 18.5 to 25 together in the ‘normal’ category, but as we know, any adult who is very thin, for example has a BMI of 20 or less, has an increased risk of having cancer or another serious wasting disease. In other words the definition of normal in this study probably included some very sick people who should not be the gold standard for health, and confused the difference between normal weight and overweight. It has already been established that mortality rises when BMI is under about 21 kg/m2 because of increased rates of cancer.

2. Quality of Life  The study only concerns the age at which people die and says nothing about the quality of life when they are alive. There is clear evidence that rates of diabetes, heart disease, arthritis and other painful, difficult diseases are much higher in overweight and obese people compared to those of ideal weight. According to this new study, they may not result in dying earlier if people are overweight, but these diseases still occur and have a clearly negative impact on rates of disability, quality of life, functionality in life, and cognitive abilities.

What most people want is to live healthy, with their mind intact for as long as possible, rather than live a long time in a disabled state. This means that losing weight for health is still an important goal. Quality of life was not the subject of this new JAMA study.

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