Exploring the Science: “Fat but Fit” & Metabolic Health

Have you heard of the phrase “fat but fit”? It’s the idea that you can be healthy even with large amounts of extra weight. It is somewhat controversial in medical and public health communities because we don’t want to stigmatize people for having extra weight but we also know that extra weight can carry health risks. In August, a study was published in the European Heart Journal which has added to the controversy. Let’s go through the details.

Who did the research? The research was primarily funded by the European Union Framework, the European Research Council, the UK Medical Research Council, the British Heart Foundation, and the UK National Institute of Health Research. There were nearly 50 researchers from many institutions across Europe including Imperial College London, University of Ioannina, University Medical Center Utrecht, German Cancer Research Center, and University of Cambridge.

Who did they study? The participants were part of the European Prospective Investigation into Cancer and Nutrition cardiovascular disease (EPIC-CVD) case-cohort. A case-cohort is a study where a group of people are identified and followed over a period of time but are not given any intervention. The researchers look at the different things they are exposed to, such as diet choices, work environments, smoking, and alcohol use, to see how it affects their risk of diseases or negative health outcomes.

The EPIC-CVD group included 366,521 women and 153,457 men, mostly aged 35 to 70 years old when they were recruited between 1991 and 1999. They were recruited at 23 centers across 10 European countries: Denmark, France, Germany, Greece, Italy, the Netherlands, Norway, Spain, Sweden, and the UK.

The participants that were used for this particular study were a sub-group of 17,640 people who were randomly selected from the full EPIC-CVD group and who did not have any history of stroke or heart disease.

What did they study? The researchers followed the sub-group for an average of 12.2 years to see how many people developed heart disease. They wondered what the connection was between body fat, metabolic health, and the development of heart disease.

How did they try to answer their question? The participants completed questionnaires and gave blood samples to have their cholesterol and blood sugar measured. They also had their blood pressure, weight, height, and waist circumference measured.

The researchers used this information to determine how many of the participants were “metabolically unhealthy”. A participant was considered metabolic unhealthy if they had 3 or more of the following criteria at the start of the study:

  • high blood pressure, use of blood pressure medications, or self-reported history
  • high triglycerides or use of lipid-lowering medication like statins
  • low HDL (good) cholesterol
  • high blood sugar, use of diabetes medications, or self-reported history
  • high waist circumference

Obesity was defined as BMI > 30 and normal weight was BMI < 25.

When they looked at results, they used statistical models to make sure that other lifestyle factors weren’t affecting the risk of heart disease. They adjusted for these types of factors: country, gender, age, education, smoking status, alcohol intake, diet and physical activity.

What did they find? They found increased risk of heart disease for two groups of people: people with obesity who were metabolically healthy and people with normal weight who were metabolically unhealthy.

We can think of people who were metabolically healthy and normal weight as our lowest risk group. Compared to this group, people who were metabolically healthy with obesity had a 28% increased risk of heart disease. People who were metabolically unhealthy with normal weight had double the risk of heart disease compared to the lowest risk group.

What does this mean?  Having obesity, even if you are healthy now, means that you are at an increased risk for heart disease compared to someone at a normal weight. There are many people with obesity who will not develop heart disease but it is a risk factor that we must take into account. However, just being at a normal weight doesn’t make you healthy. If you are at a normal weight, you still need to think about the metabolic health criteria: blood pressure, triglycerides, cholesterol, blood sugar, and waist circumference.

When I work with people who are thinking about losing weight, we always talk about what a healthy weight means to them. It’s not realistic or healthy for everyone to be at a normal weight and we can’t pretend that just being at a normal weight will solve everyone’s health and life problems. This study shows us that having poor metabolic health (regardless of weight) is actually more risky than having obesity. On the other hand, we also can’t ignore the impacts on the body from carrying too much extra weight. It’s why I individualize goals to find a healthy and realistic weight range for each person.