Obesity Threat to Health of Individuals and Populations May Be Underestimated

MedicalResearch.com Interview with:

Ching-Ti Liu, PhD Department of Biostatistics Boston University School of Public Health Boston, Massachusetts

Dr. Liu

Ching-Ti Liu, PhD
Department of Biostatistics
Boston University School of Public Health
Boston, Massachusetts

MedicalResearch.com: What is the background for this study? What are the main findings? 

Response: Being overweight and obese are increasing worldwide and this obesity epidemic threatens to reverse the gains in life expectancy achieved over the past century. However, many investigators have observed, paradoxically, that overweight individuals are associated with a lower mortality risk. These results may suffer from a potential confounding due to illness or reverse causality in which preexisting conditions may alter both body weight and the risk of death.  Recently published studies have tried to mitigate this reverse causal bias by implementing sample exclusion and they came to a different conclusion: between BMI and all-cause mortality there is an increased risk of death for the entire range of weights that are in the overweight and obesity ranges.

However, the elimination strategies may lead to the loss of generalizability or precision due to over-adjustment. In addition, the traditional investigations have only utilized a subject’s weight at a single point in time, which makes it difficult to adequately address bias associated with reverse causality.

Currently, the idea incorporating a subject’s weight history has been proposed to deal with the concern of reverse causality, but the existing works had been based on a subject’s recall or self-reported data, which may lead to misclassification and, therefore, result in overestimating the risk of mortality.

To help assess the relevance of being overweight or obese to the risk of death in the general population, we conducted a prospective study, using an individuals’ maximum BMI before the beginning of survival follow-up instead of their weight status at a single point in time, using data from the Framingham Heart Study (FHS).

We observed increasing risk of mortality across various BMI categories (overweight < obese I < obese II) relative to normal weight using maximum BMI over 24 years of weight history.

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Brain Reward System Underactive In Some Overweight People

Dr. Agatha van der Klaauw, PhD Wellcome Trust Postdoctoral Clinical Fellow Wellcome Trust-MRC Institute of Metabolic Science University of Cambridge Metabolic Research Laboratories Addenbrooke's Hospital Cambridge, United KingdomMedicalResearch.com Interview with:
Dr. Agatha van der Klaauw, PhD
Wellcome Trust Postdoctoral Clinical Fellow
Wellcome Trust-MRC Institute of Metabolic Science
University of Cambridge Metabolic Research Laboratories
Addenbrooke’s Hospital
Cambridge, United Kingdom

 

Medical Research: What are the main findings of the study?

Dr. van der Klaauw: Obesity occurs when we eat more calories than we burn which is often easy to do as many foods are highly palatable and high in calories. Highly palatable foods such as chocolate trigger signals in the brain that give a feeling of pleasure and reward (sometimes called cravings) which can contribute to overeating. These signals are processed in the reward centres in the brain, where sets of neurons release chemicals such as dopamine. However, very little is known about whether the reward centres of the brain work differently in some people who are overweight.

In this study, we were interested in studying overweight people who had a problem with the melanocortin 4 receptor (MC4R) gene. About 1% of obese people have a problem in this gene which contributes to weight gain from a young age. We compared three groups of people: people who were overweight due to a problem in the MC4R gene, people who were overweight but the gene was normal and some people who were normal weight. We performed functional Magnetic Resonance Imaging (fMRI) scans to look at how the reward centres in the brain were activated by pictures of appetizing food such as chocolate cake compared to bland food such as rice or broccoli and non-food items such as staplers.

We found that in normal weight people, the reward centres are activated (light up) when they are shown pictures of cake or chocolate and the same was seen in overweight people with a problem in the MC4R gene. But we found that the reward centres were underactive in overweight volunteers (in whom the gene was normal).

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