Imagine you get onto a crowded tube train. A mother and child are next to you standing slightly squashed between the doors and the hoards of people now crammed into the carriage. You hear the frustrated child say to their mum,
“Why is it so crowded in here?”, only to have the mother playfully reply,
“It’s crowded in here because more people got on the train than got off!”.
Whilst in jest, this response obviously doesn’t answer the question, why the crowd? It actually just rephrases the problem: too many people are on the train. The reason that the train is crowded is that it’s rush hour. Rush hour is a reason, not a re-summary of the situation…
So why the scenario? Well, the prevailing explanation of why we get fat follows the same logic. Telling someone they’ve eaten too much and burned too little says nothing of the causes of their fat accumulation. All you’re doing is restating the problem in a different way: they’re overweight because they’ve stored more calories than they have burned. The train is busy because more people got on than off. Just like the naive child in the story, our society has innocently accepted this non-explanation for obesity. So, if rush hour, not net-change in people causes overcrowded trains, what’s the cause of people getting fat? Hint: it’s not eating too much and exercising too little.
Essentially, being fat is a problem of why your body is holding on to those additional calories instead of using them. Obesity can be thought of as a disorder in energy regulation. So to answer why we get fat, we need to uncover what regulates our energy use, and why it leaves us fat not lean, why we might store calories not burn them.
In biology, we fundamentally look to hormones when seeking to explain how the body regulates itself. We have a huge number and variety, and are very much still discovering how they all interact and interplay. It would be litotic to describe endocrinology as complex, indeed when you get down to it, we hardly get how the body works at all. Despite our limited understanding, we do now know, as of progress which began in the early 20th century, that insulin is the primary hormone controlling fat storage in the body. To put an extremely long and complicated story short, in which we’re still working on many of the details and exact mechanisms, more insulin = more fat storage. Correspondingly: less insulin = more fat burning. If you want to know how to control your insulin levels, thereby controlling your body fat, it’s useful to know that dietary carbohydrates are the main stimulus for insulin secretion. Thus, limit carbs, and you limit your body fat. I deal with this a little more in my other article: Let Me Tell You Why You’re Fat. Not all carbs are made equal, the more complex and low Glycemic Index (GI) they are the less dramatic the effect on your insulin secretion, but I digress.
Despite the lack of success associated with eating less and moving more, a lot of people have claimed the calories-in / calories-out hypothesis for weight loss must be true because of the 1st Law of Thermodynamics. This law basically says that you can’t destroy energy, just convert it to one form or another. You can’t get fatter if you’re not taking in more energy than you’re expending. For years any theory that challenged this hypothesis was limited to the realms of quackery, after all, much of modern physics is built upon these laws- to deny them was to go against modern science. Low-carb diets were confounded because they “broke” this elementary law, people could eat their fill of low-carb foods and still lose weight. But the first law of thermodynamics has little relevance to energy regulation as our body is not a closed system. Essentially, there are many, many ways to burn calories and expend energy as a living, breathing being (e.g. constant heat loss, energy spent digesting food, expelling ketones in urea, inefficient digestion, building muscle etc.).
In an attempt to make calorie burning outweigh energy intake, as per the erroneous conventional wisdom above of calories-in / calories-out, many people turn to exercise. After all, if the hypothesis were true, exercise would unequivocally help with fat loss. It turns out that exercise is a great wellness tool, but unfortunately it is hardly any help with weight loss.
Are you kidding? Surely if I burn calories they have to come from somewhere?
And they do. Providing you haven’t just eaten a huge meal the likelihood is that you will burn some body fat if you exercise effectively (think HIIT and strength training). Unfortunately for dieters that’s not the end of the story.
Enter Lipoprotein Lipase (LPL) and Hormone-Sensitive Lipase (HSL).
This isn’t as complex as it looks. Biologically speaking, LPL is responsible for pulling energy in the form of glucose from the blood and storing it in cells as fat. Conversely, HSL works to make us burn energy by encouraging stored fat in cells to be broken down, sent into circulation, and used. When we work out, unsurprisingly given the above logic, LPL activity increases in our muscle cells and decreases in our fat cells. Our muscles get energy hungry and our fat cells don’t. Simultaneously to the action of LPL, HSL decreases efforts in our muscle cells and increases in our fat cells. When you think about it this all makes sense; we want to break down fat from storage and get it to muscle cells so it can be used for energy. So from exercising we’ve lost a bit of weight, as we’ve burned a little fat. Whoever said exercise doesn’t help?
Not so fast.
The caveat to this story is what happens next. When we finish our workout, as we inevitably will, the actions of LPL and HSL reverse. Suddenly, your fat cells want to recover the energy they have just lost, so LPL activity increases in fat cells and halts in muscles. HSL, the enzyme which breaks down intracellular (“inside the cell”) fat also gets downregulated (biology-speak for reduced). As a result, your fat cells refuel, and you regain your “weight”. Ah.
But wait, what if I don’t eat after my workout?
Then yeah, you’ll spot the energy deficit by catabolizing skeletal muscle, not just body fat. Way to go. You just lost some lean tissue, not a good thing, seeing as lower lean mass is linked to higher mortality. Additionally, not eating after exercise is difficult, given the inevitability of a correspondingly increased appetite. So maybe we can say instead that exercise does help you lose weight, if you can bare willingly eating less than you need to long term (you will eventually fail), particularly after exercise, and don’t mind losing muscle in the mix. Clearly this is not an optimum weight loss strategy, especially given that regularly eating less than you need to makes your body more careful with the calories you do get by down-regulating your metabolism.
The idea that you can just exercise more to lose weight without an associated increase in hunger (if not immediately then at some point later in the day) is erroneous. Hunger is a physiologically rather than psychologically controlled feeling. So you may “burn calories” but you’re more likely to eat more to compensate, especially with the complex self rewarding people do post-exercise. Weight loss takes time, and most people find it considerably difficult to consistently undereat whilst increasing exercise or physical output. So exercise is unhelpful for fat loss. Need a study to back it up? There are many good ones. Here’s one.
I must add that I would never want to stop anyone from exercising. It has many other benefits– on circulation and brain function for example. Just remember if you want to lose fat, diet is key.
Disagree? I don’t blame you, this is hard to swallow.
Have your say, leave a comment.