A European study has claimed that the concept of being ‘fat but fit’ is a myth. The study found that people who are obese but metabolically healthy had a 28% higher risk of heart disease than people who are a normal weight. What is the evidence behind the ‘fat but fit’ claim and counter-claims?
Metabolically healthy obese
Being ‘fat but fit’ is when someone is metabolically healthy obese – they have a body mass index (BMI) of over 30, and are therefore classed as obese, but do not have any initial signs of associated health risk factors such as high blood pressure, diabetes or high cholesterol.
A recent Europe-wide study has claimed that the concept of being ‘fat but fit’ is in fact a myth. This follows an earlier British study that had similar findings.
This latest research, by Imperial College London and the University of Cambridge, analysed data from over 17,000 people across Europe. The BMI of each person was calculated, they had to complete a questionnaire about their medical history, diet and lifestyle, and tests were done on their metabolic health, such as measuring cholesterol, blood sugar and blood pressure.
For the next year they were followed up to look for any signs of heart disease.
The findings showed that BMI was a risk factor for heart disease, regardless of the person’s metabolic health. Those whose BMI meant that they were classed as being obese, but were metabolically healthy (‘fat but fit’), had a 28% higher risk of getting coronary heart disease than people who were a normal weight and metabolically healthy.
Those who were overweight (rather than obese) and metabolically healthy had a 26% higher risk of coronary heart disease.
Coronary heart disease happens when the coronary arteries become narrowed because of a build-up of fatty material. The main symptoms are angina, heart attacks and heart failure.
The study, which was published in the European Heart Journal, concluded: “These findings challenge the concept of ‘metabolically healthy obesity’, encouraging population-wide strategies to tackle obesity.”
A previous study by researchers at the University of Birmingham looked at the GP records of 3.5 million people in the UK. Again they looked at their BMI and whether they had any metabolic conditions, such as diabetes, high blood pressure or abnormal blood fats.
This study found that people who are metabolically healthy but obese were 50% more likely to get heart disease, 7% more likely to get cerebrovascular disease (including a stroke) and twice as likely to have heart failure.
The study also found that the risk of heart conditions in people who are obese increased with the number of metabolic abnormalities (for example having diabetes and high blood pressure) they have.
Highest risk of heart disease
The European study found that metabolic health is still the most important risk factor for heart disease. Normal weight people who were metabolically unhealthy had more than double the risk of heart disease than normal weight people who were metabolically healthy. Therefore demonstrating that it is possible to be ‘not fat but unfit’.
The researchers said: “Irrespective of BMI, metabolically unhealthy individuals had higher coronary heart disease risk than their healthy counterparts. Conversely, irrespective of metabolic health, overweight and obese people had higher coronary heart disease risk than lean people.”
The lead researcher from the British study, Dr Rishi Caleyachetty, agreed, saying that: “At the population-level, so-called metabolically healthy obesity is not a harmless condition and perhaps it is better not to use this term to describe an obese person, regardless of how many metabolic complications they have.”
Obese and healthy
So where did the ‘fat but fit’ theory come from? There have been studies that demonstrate this to be a possibility. For example, a study published last year showed that older people who are overweight live longer than those who are normal weight. And previous research has suggested up to one in three obese people are healthy.
However, these two new studies refute these claims, and appear to confirm that being obese in itself increases the risk of heart problems, regardless of metabolic health.