The nature of the link between obesity and diabetes

obesity and diabetes

Can obesity cause diabetes or cardiovascular disease? And if not, how are they related? These are questions looking for answers, and a small piece of the puzzle fell into place last week.

A new systematic review and meta-analysis, published in JAMA Network Open, is the first-ever meta-analysis pooling data from studies conducted with a technique called Mendelian randomization1 which employs genetic markers and number crunching to mimic a clinical trial.

Cleveland Clinic Newsroom: Cleveland Clinic genetic analysis links obesity with diabetes, coronary artery disease

Mendelian randomizations are less reliable evidence of causation than randomized clinical trials, but they are much less expensive to conduct, and are better evidence than observational studies. The study authors explain:

Mendelian randomization offers an opportunity to study associations without many of the typical biases that are inherent in traditional epidemiologic approaches. Thus, Mendelian randomization can fill the evidence gaps by minimizing confounding, if variables are randomly and equally distributed in the population of interest.

What did the investigators find?

In this systematic review and meta-analysis of nearly 1 million participants, obesity was associated with type 2 diabetes and coronary artery disease but not with stroke… Meaning that obesity may increase the risk of subsequent diabetes and may contribute to cardiovascular outcomes and should thus remain a major focus of public health initiatives.

More specifically, each five point increase in BMI increased the relative risk of a type 2 diabetes diagnosis by 67% — a substantial connection. For coronary artery disease, the association was not as strong: a five point increase in BMI increased the relative risk of coronary artery disease by just 20%. The authors of this analysis are quick to point out that Mendelian randomization studies do not prove causality. However, they do support a causal relationship.

It’s a piece of the puzzle, and is consistent with the evidence called out in an editorial in the journal BMJ this week, entitled “The growing problem of diabetes.” In it, editor in chief Fiona Godlee writes:

Weight loss is essential for management of diabetes and can lead to remission, but once achieved it can be hard to maintain. In what may be a ground breaking randomised trial, Cara Ebbeling and colleagues found that energy expenditure was higher when people ate a low carbohydrate diet during weight loss maintenance. People randomised to a high carbohydrate diet had higher concentrations of the hormone ghrelin, which is thought to reduce energy expenditure.

At Diet Doctor, we believe low-carb lifestyles are part of the solution to the ever-increasing global burden of type 2 diabetes. Several meta-analysis of randomized clinical trials show that low-carb regimens lower the need for blood-sugar medication while improving health markers like HbA1c and blood pressure.


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  1. For more on Mendelian randomizations, Gary Taubes gave a nice explanation of how these analyses work in this MIT Technology Review article.


  1. Gentiann
    It's a lttle confusing.
    According to Dr Fung, both conditions are the result of hyperinsulinemia.
    Too much insulin circulating in the body causes insulin resistance which in turn is responsible for obesity AND diabetes type 2.
    Obesity is usually present with diabetes type 2 but not always.
    It seems that there are still many questions to be answered before jumping to the conclusion that obesity causes diabetes.
  2. Terrie
    Obesity doesn't cause diabetes it is the other way around. Obesity is often the first sign of T2....
  3. Susanne
    Yes, I agree with Terry, I have been fighting obesity all my life with some success for some Years of every diet you can think of. At 50years of age, I noticed an increase in weight no matter what Diet I went on. Now at the age 73. I have been diagnosed with T2 Diabetes. I am fighting and staying on a low Carb diet hoping this will help me .. I am on Metformin 500mg with my evening meal, high Blood meds, and 10 mg Lipitor night time. My Migraine attacks are decreasing. I have a small amount of weight loss which I would like more of, because of obesity. Weight loss seems to be so much harder as you get older.
  4. Gillian
    Combining low carb with intermittent fasting has worked for me, couldnt lose on just low carb but as soon as I started cutting out lunch a couple of times a week I have been losing albeit slowly (5k in two an half months) but still. I have my evening meal the night before at around 7.30 and then the next morning I have a coffee with a little full fat cream at breakfGast time and then no meals till around 6pm or later I havent found it at all difficult as dont feel hungry.
  5. Gillian
    Forgot to say Im almost 71.

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