Every time you see numbers on obesity, you see the Body Mass Index is being used as metric to show that obesity is getting a bigger and bigger problem. The Body Mass Index is basically a body length corrected measure of body weight. When diets go head to head, “losing weight” is used as measure of success. When making a choice between a Paleo diet, a Keto diet, a vegan diet, a Mediterranean diet, etc, etc, people will often ask the question: “What diet is best to lose weight”, and many a proponent of whatever diet he/she is trying to sell, will go out of his/her way to show how successful the diet is at helping you lose weight. High number for body weight and BMI have become synonymous to obesity and with all obesity related illnesses. As such, the concept of “loosing weight” has become synonymous with the idea of improving health and a way for obese people to stop being obese. In this article I will show how not only BMI and body weight are poor measures for obesity, but also that the focus on loosing weight is actually a major contributor to the obesity problem. A contributor that is creating a situation where people are discouraged from continuing the most effective obesity measures. A contributor also that is creating an increasing number of low-BMI obese people, creating a situation where the true size of the obesity epidemic is being obscured from sight.
A linguistic problem?
Obesity is a term that describes a person having unhealthy levels of body fat. That is, as a term, and as a medical problem, obesity is about body fat. Looking at actual health problems in fact and their correlation to body fat levels, it may even be fair to sat that as a medical problem, obesity is about high levels of visceral body fat. Visceral fat is the part of our body fat that resides within the abdominal cavity around our internal organs. Having massive love handles may not be aesthetically pleasing, from a health perspective there are to my knowledge no convincing studies showing the existence of independent risk factors from subcutaneous fat.
So let’s recapitulate. We have medical issues that are strongly correlated with visceral fat levels. We have visceral fat levels that are correlated relatively strongly with total body fat levels, and we have total body fat levels that are relatively poorly correlated with total body fat levels.
If we assume the lack of evidence of independent correlations excludes the possibility of causality, than a likely correlative diagram like the one on the right is probably pretty much accurate. We have a possibly causal link between visceral fat levels and a wide range of medical issues. It is also still possible that both the medical issues and visceral fat levels simply have a common cause, but if there is a causal link between obesity and health issues, this is where we will find it.
Next, there is a strong correlation between visceral fat levels and total body fat levels. This correlation obviously flows two ways.
Finally there is a correlation between total body fat and body weight. Fat has weight, so more fat mass obviously means more body weight, yet much of a person’s body weight is made up by other things than fat. As BMI is a measure of body weight, we get the diagram here on the right. So why do we measure obesity with BMI? And more importantly, why do we refer to obese people as being overweight, while weight is so indirectly and weakly linked to the actual obesity related medical problems? And worse, why do we urge obese people to make changes primarily to their BMI by means of “loosing weight” ? Given that what we care about appears to be percentage driven, does it even make sense to lose weight if we don’t differentiate between the components tat make up our weight. In fact, we could possibly improve body fat and visceral fat levels by increasing our weight in the right way.
Obesity is not a weight problem, it is a visceral fat problem at best. Visceral fat as percentage of total body weight if we trust the data. We should stop using weight and BMI as measure of obesity. We should stop referring to obese people as being “overweight” and we should most pressingly stop referring to personal attempts at reducing obesity as “loosing weight”.
A sad story
A friend of mine, just about a year ago decided to try and make a change is his life. He had been fighting obesity for many years, but after we spoke about my approach, he decided as a new-years resolution to give a low-carb high caloric diet combined with a rigid strength training program a try. Four and a half months into the program his visceral fat levels were down by a whopping 6%, his total body fat level by 8%. Seriously, I dream of having such amazing progress myself, I had never seen anyone react that well to a strength first approach. His progress wasn’t just in these numbers, it was really starting to show. Than disaster struck. After having visited his GP first and a dietician second, my friend stopped going to the gym. A few months later I ran into him again and asked him why I never saw him any more in the gym. What happened was that his GP had tried to convince him his BMI was getting to high (apparently the added muscle mass had tipped his BMI just above an alarming level), and had send him to a dietician. That dietician had consequentially convinced him that body composition machines at the gym were inaccurate, that his daily caloric intake was more than 1000 calories to high, and that switching to a low caloric low fat diet in order to get his BMI back to a healthy level would be the only sane thing to do. I tried to tell him that while I am just a lowly engineer and no health profesional, the mirror didn’t lie to him, I seemed to be getting trough to him for a moment, but than after some thought he just said to me: “Sure, your diet and workout did make me look and feel better, but I rather lose weight and avoid the health problems with being overweight”. I couldn’t think of anything to say at that moment. Unable to even comprehend the reasoning and the level of disconnect. We are collectively so obsessed with body weight that even dropping a full 6% from visceral fat levels in just four and a half months, looking much better in the mirror and most importantly feeling better isn’t sufficient to convince us that our BMI going up half a point in the process may not actually be a problem. Not just that, health professionals are clinging to these numbers as if they are the one and only variable that has any meaning.
The dangers of loosing weight
If we look at loosing weight, the most common way to do it is to go on a diet that leaves you with a caloric deficit. Something that to the human body would be close to indistinguishable from famine. If we look at the data from the China Study II, a data set created almost 30 years after the great Chinese famine, we see some shocking correlations in the data set. The correlation between people who suffered from the Chinese famine and all cause mortality for the 70-79 age group is very much presents and has an order of magnitude that should definitely be taken seriously. We shouldn’t jump to conclusions, but even if artificial famine may bring down visceral fat levels to safe levels, what new dangers is it creating in our bodies?
An other issue with loosing weight lies in the loss of muscle mass and the impact on your metabolic rate. The numbers differ depending on who you ask, but a kg of muscle mass will burn the energy equivalent of about a teaspoon of sugar a day just sitting still. On the wrong diet, especially the pseudo-famine diets that promise to make you lose weight in record time, loosing 20 kg of body weight could easily set you back 6 or 7 kg of lean muscle mass. That is 6 or 7 teaspoons of sugar worth of energy per day. Now guess what happens when you end your diet and start eating the same you ate before your diet. While before you started dieting your body may have been in something of an energy equilibrium, if you now consume the same, you will now end up with an energy surplus of about 100 calories. A 100 calories surplus may not sound as much, but it adds up to about 4kg of new fat a year. And that is on top of the surplus you already had that made you end up in a situation where you wanted to lose those 20kg in the first place. So if it took you 5 years to gain those 20kg in the first place, this time two and a half years will end up doing the trick. Realizing that 3 kg of muscle mass will burn the energy equivalent of 2kg of fat mass every year should make you think twice about allowing yourself to lose substantial amounts of muscle mass. If anything you should try to gain muscle mass.
Now repeat the cycle a few time, as many people end up doing. The fourth time you lost that 20kg, your lean body mass is bound to be so low that even with a BMI of 21 your body fat percentage is off the scale. In the BMI based statistics however, you won’t show up as obese, next year you might, but this year you are on the bottom of your roller-coaster ride. You will be part of the hidden part of the obesity epidemic. But not just people who repeatedly starve themselves are hidden obese. Many people who don’t work out and eat junk food all the time don’t have any “weight” problem and may even look skinny but have such high levels of body fat that they should be considered obese. So none of the aesthetic issues with obesity but all of the health risks.
Fat mass and muscle mass
The best way to visualize the disconnect between BMI and obesity is using a simple graph. Lets take a highly simplified body composition consisting of muscle mass or non-fat mass and fat mass. We take the muscle mass or non-fat mass of a person as X-axis, and use the Y-axis for body fat mass. Now you can describe a person’s body composition with a simple vector that points from the origin of the graph to the point with the persons fat and non-fat mass. We can also, for any given age/gender draw a straight line depicting the ideal body fat percentage for our person. Now for obesity. You can say that obesity is quantified by φ , then angle between our persons body composition vector and the ideal body fat line.
As for the BMI, how does BMI fit into all of this. Well imagine we use the same graph to show whe body composition of a thousand random and mostly sedimentary people of the same body length. Than from those people we look at those with an ideal body fat percentage and take the average body weight of that subgroup to scale our whole graph with.
Now we end up with a graph where BMI is defined relative to the magnitude of the vector on our scaled graph while obesity is defined relative to the angle of the vector. For anyone with even an elementary understanding of mathematics, using |V| as stand in for φ should be complete and utter madness. Apparently however for many nutritional and health professionals there is nothing wrong with doing so.
If we truly want to fight obesity, the whole “weight loss” mantra should be considered harmful. Instead of focusing on weight loss and on BMI, a healthy non obese person combines healthy body fat levels with decent muscle mass and bodily strength. In fact, you can fight obesity and be gaining weight. By gaining muscle mass, your resting metabolism will go up, not by much but still a significant teaspoon of sugar a day that will add up over time and will help to keep off any body fat you end up loosing in the process. Picking a proper diet will help shift your bodies fat deposit shift from visceral to subcutaneous, all adding to a better body composition. Refined grains, fructose and trans fats for example are linked to higher partitions of bodily fat being stored as visceral fat. Until we realize that obesity is about percentages, about the location of our bodily fat and hardly about weight or BMI, and until we stop looking at weight loss as a cure for obesity, there is no way we can even begin to address the issue. No “this diet will help you lose weight” is even relevant to reducing obesity in the end. You can have a BMI of 21 and be obese, or you can have a BMI of 38 and not be obese, and while BMI can be a useful tool for looking at whole populations, for individuals who need a metric to track progress with, BMI should be considered harmful. If you are obese, you are overfat, not overweight. Your weight is completely irrelevant to the condition of obesity at least as far as medical risk factors are concerned. So don’t ask “What is the best way to lose weight?”, weight is irrelevant, instead ask “What is the best way to improve bodily composition?”. Once you understand that asking the wrong question will give you the wrong answers, you can start making the mental switch that allows us to actually address the obesity problem. Lose visceral fat, gain muscle mass and get stronger. If in the process you lose weight, fine. If in the process you actually gain weight: even better.