Beyond BMI: How to more accurately assess metabolic health
The Body Mass Index (BMI) is the standard measure for determining whether a person is at a healthy weight. BMI is calculated as weight in kilograms divided by height in square meters, and specific thresholds are set to classify people into weight categories.
- 2 is underweight
- 5 to 25 kg / m2 is a “healthy” weight
- 25 to 30 kg / m2 is overweight
- > 30 kg / m2 is obese
BMI doesn’t tell you anything about body composition, which is far more important. Also, even regardless of body composition, you can be at normal weight and be extremely unhealthy metabolically – referred to as “thin outside fat on the inside” or TOFI; and you can be overweight and perfectly healthy – so called “metabolically healthy obese” or MHO. whether you are metabolically healthy or not.
The concept of body composition is quite simple: it’s not the weight that matters, but whether that weight is muscle or fat. A classic example is that of Dwayne “The Rock” Johnson. We look at the man and we see that he is not too fat, and yet his BMI of 34.3 kg / m2 makes him “obese”. Obviously, this is an extreme example, but it shows that BMI is an over-simplified measure for health. In fact, high muscle mass is one of the best predictors of health, especially in men. So, should we prescribe weight loss for people who are overweight but closer to the Dwayne end of the spectrum? Probably not.
TOFIs, aka skinny and fat people, are the reverse of “Dwayne”. Typically, about 20-25% of people are “TOFI”, which means they show signs of metabolic syndrome and insulin resistance at normal weight. In fact, about 15% of people with type 2 diabetes are at a “healthy weight”. In fact, TOFIs who develop type 2 diabetes even seem to be at higher risk for heart disease than overweight people with the condition. Let’s decompress this a bit more.
Some TOFIs simply have low muscle mass. As we said above, muscle mass is healthy, metabolically active tissue that interacts with fat and is also the primary sink for blood glucose. This is why people with large muscles can consume a lot more carbohydrates while experiencing a lower rise in blood sugar. But being TOFI isn’t just about body composition, it’s also or you store your fat. Just like in real estate, fat is a matter of “location, location, location”.
The body has two main types of fat: subcutaneous fat and visceral fat. Subcutaneous fat is the type that is found under (under) your skin (dermal). Visceral fat, on the other hand, sits inside your abdominal cavity and around your organs. Visceral fat is extremely pro-inflammatory, and excess visceral fat can contribute to metabolic dysfunction and insulin resistance. And some TOFIs, although they are “healthy” in weight, carry a lot of visceral fat, predisposing them to adverse health effects.
Then there are the Metabolically Healthy Obese (MHO). About 15% of obese people have MHO, and not all of them look like Dwayne Johnson. In fact, some look quite big. However, they can exhibit excellent metabolic markers and live long healthy lives. Indeed, in general, MHOs transport their fat in the form of subcutaneous fat rather than visceral fat. They can gain weight, but the body stores fat in a relatively healthy way. In fact, you can even recapitulate the MHO phenotype in mice by simply overexpressing GLUT4 glucose transporters in subcutaneous fat cells of mice. These mice get incredibly fat, while remaining perfectly healthy. The point to remember is that it depends less on how much fat you have, but where your body is putting it. And we are all bio-individuals in this regard.
Other markers of metabolic health
Now for the most important question, if BMI is an inaccurate measurement for many, how do you rate metabolic health? There is certainly no single answer or medical consensus on this subject. So the following represents my opinion, not medical gospel or advice.
The first and simplest measure is the “string test “ for visceral fat. Take a piece of string the length of your waist. Then fold the piece of string in half and wrap it around your waist. Waist circumference is an indicator of visceral fat, and if the two ends of the string are struggling to meet, your visceral fat level may be too high. If so, one of the easiest ways to reduce visceral fat is to eat a diet low in carbohydrates and high in healthy fats.
To track your health progress, you can cut the rope at your current waistline, and then as you progress on a low-carb diet, see if you can make the rope shorter and shorter. . Sometimes I see people “taking” the ropes test week after week, even though their weight is barely changing or not changing at all. And, if you want a more advanced test, you can get a DXA scan for body composition and visceral fat content.
There are also blood markers that might be relevant to track. On a standard fasting lipid panel, triglycerides and HDL cholesterol is the most important marker of metabolic health. High triglycerides (> 150 mg / dL) and low HDL ( 50 mg / dL.
In those who do not have diabetes, fasting insulin is a good marker of metabolic health. Elevated fasting insulin in non-diabetics suggests the development of insulin resistance and metabolic syndrome. Experts have different opinions on what constitutes good fasting insulin, but I and most of the doctors I work with suggest a level HbA1c could be a better marker to follow and levels
Finally, I like to assess energy. It is a subjective measure. Do you feel full of energy? Do you want to move your body? A metabolically healthy body is one that likes to move, just like a stallion likes to run. Scans and blood markers can be informative, but your subjective assessment of physical energy can also be a great functional “test”. Plus, at the end of the day, quality of life matters most.
Improve metabolic health
88% of American adults have at least one marker of metabolic syndrome. Randomized controlled studies have shown that even controlled for calories and protein, low-carb diets are better than low-fat or mixed diets at reversing metabolic syndrome (Hyde et al. 2019). Therefore, a well-formulated low-carb or ketogenic clean form of diet might be a good option for those looking to regain metabolic health.
Resistance exercise also helps promote metabolic health. Building muscle can not only improve body composition, but it can also help burn visceral fat and improve blood sugar control. Two sessions of high-intensity weight lifting or strength training per week are sufficient for most people. Focus on quality over quantity. Aerobic exercise is another tool that can improve metabolic health. Although this does not necessarily lead to weight loss.
BMI is a poor indicator of health. It effectively stereotypes people into health categories, without further consideration of how weight is distributed, whether in muscle, subcutaneous fat, or visceral fat. Because we are all individuals, we all have different “healthy” BMIs. If you want real health, look beyond BMI. And, if you achieve metabolic health, it’s just possible that your BMI will drop as a side effect.
Conferences and listening
Insulin resistance podcast with Bret Scher, MD and Benjamin Bikman, PhD
Interpretation of lipid panels with Paul Mason, MD on Youtube
LowcarbMD: Minds on Visceral Fat Meet with MD and Three Doctors