Does metabolically healthy obesity exist?
Since the 1980s there have been numerous reports that some people remain metabolically healthy despite becoming overweight or obese. What is meant by this?
A metabolically healthy obese individual is a person with a body mass index (BMI) over 30 kg/m2 who does not present clinical or laboratory signs of chemical (metabolic) abnormalities in the body. This is still a very grey area, but here are the conclusions I believe we can draw from the currently published evidence and knowledge on the subject.
- A proportion of obese individuals maintain a state of metabolic health closer to that of healthy normal weight individuals
- Such individuals are less likely to develop obesity-related disease.
- This situation is probably transient and, unless weight is controlled, most (though not necessarily all) will eventually become metabolically unhealthy, with the consequent increase in the risk of obesity-related diseases.
- There is no test that will determine who will develop metabolic changes, or when.
- We must encourage any person with overweight or obesity to consult a health professional in order to keep their risk of future disease as low as possible.
- From an administrative point of view, the limited budget and finite resources of the NHS mean we must target our therapeutic actions. More intensive (and therefore higher risk) therapies, which are also more costly, should be directed at those patients at greatest risk. However, this does not mean we can ignore patients at lower risk.
What it means to you?
If you are overweight or obese, you probably have metabolic alterations that could predispose you to developing chronic disease. You should act now.
Even if you do not have metabolic disturbances at the present time (i.e. you are metabolically healthy), it would appear likely that at some point in the future you will develop metabolic abnormalities that put you at risk. There is no way of knowing if you could be one of the few to remain metabolically healthy for longer, so take steps now to improve your diet and lifestyle, and keep your risk down. In addition, whilst you are metabolically healthy, the treatment of obesity using dietary and lifestyle measures should be easier, because when metabolic changes occur, they provoke a vicious circle that makes you hungrier as you become heavier.
If you would like a more in-depth analysis of this subject, please read on.
The first step must be to define health status in obesity
Before we consider metabolic health, we must exclude those patients with existing obesity-related disease, including:
- Physical conditions such as joint pain, varicose veins, sleep apnoea, heartburn, urinary incontinence and functional limitations in the activities of daily living
- Nutritional deficits (numerous vitamin and mineral deficits may be detected)
- Mental health disorders, such as depression
- Organic diseases (chronic diseases affecting the heart, lungs or liver, as well as high blood pressure, atherosclerosis, diabetes, cancer…)
(Read more about obesity-related disease here.)
Only then can we consider the metabolic abnormalities that typically arise with obesity. The following criteria have been used in research in this field.
- Metabolic syndrome (diagnosed by the presence of any 3 of the following):
– abdominal obesity defined as a waist circumference >102 cms (40 inches) in men or 90 cms (35 inches) in women (these figures vary between ethnic groups)
– high blood pressure (>130/85 mmHg) or on antihypertensive treatment
– high blood sugar levels (fasting blood sugar >5.6 mmol/L [100 mg/dL])
– high blood triglyceride levels (>1.7 mmol/L [150 mg/dL])
– low HDL-cholesterol levels (men <1.04 mmol/L [40 mg/dL]; women <1.3 mmol/L [50 mg/dL])
- Tests of insulin resistance: A high blood sugar level is a sign of insulin resistance (the insulin is not acting to its full effect). Certain tests, such as HOMA-IR and HEGC, analyse insulin resistance more precisely.
- Signs of atherosclerosis (thickening of the arteries that can cause blockage):
– Increased thickness of the lining of the carotid arteries in the neck (carotid artery intima-media thickness)
– Calcium deposits in the coronary arteries (coronary artery calcium score)
- Inflammatory status: This is assessed by a blood test that measures molecules that the body uses to signal inflammation.
As you can see, a wide range of criteria has been used, and research groups vary considerably in which ones they apply to define metabolic health. This would explain the differences in the proportion of obese persons reported as metabolically healthy, varying from 0% to over 40%.
Outcomes are also affected, as obese persons who fulfil more strict criteria of metabolic health criteria appear less likely to develop illness. This statement is backed up by Canadian and UK studies. However, a more recent, very large 6-year study in the UK showed significantly higher rates of ischaemic heart disease, heart failure and stroke in the metabolically healthy obese group compared to metabolically healthy normal weight individuals, even in those in whom a very strict definition of metabolic health was used.
According to some studies, the risk of diabetes in metabolically healthy obese individuals is still about 4 times higher than in the metabolically healthy normal weight group. But once metabolic alterations develop, the risk is increased 20-fold.
We need consensus on the criteria to identify metabolically healthy obesity. At present, most research is based on the absence of metabolic disease, dyslipidaemia or hypertension, but there is little consistency even with these limited criteria.
Genetic and epigenetic studies, analysis of markers of inflammation, liver fat content, plasma free fatty acid levels, the gut microbiome and other criteria need to be studied to find more specific markers of metabolic health. These will enable us to establish a universal definition of metabolically healthy obesity that will identify those at highest risk of developing the complications of obesity and thus target our resources and therapeutic actions more rationally and more effectively.