Read through any article that embraces the validity of the Calories In, Calories Out (CICO) model for weight loss, and you’re bound to come across comments like: “Wrong. All you need to care about is insulin production. If you keep your insulin levels low, you’ll lose weight. Truth is, the total number of calories you eat doesn’t matter.” And then, right on cue, they’ll bring up the carbohydrate-insulin model of obesity — which proposes that insulin drives nutrients to be stored as fat, thus leaving the rest of the body with low energy, causing individuals to overfeed.
Well. Truth is, while hormones do play a critical part in the regulation of body weight, it is incredibly simplistic and naive to single out insulin as the sole contributor. To understand why we need to take a deep-dive into the science behind insulin and the carbohydrate-insulin model of obesity. So, grab those nerd glasses (and possibly a cup of coffee!) and follow along. It’s going to be a wild, evidence-based ride.
What is insulin, anyway?
Insulin is a hormone made in your pancreas, a gland located behind your stomach. And one of its main roles is to help regulate blood sugar levels. But — how? Well, when you eat, the carbohydrates in your meal is broken down into glucose, which elevates your blood glucose levels. This, in turn, signals your body (more specifically, your pancreas) to release insulin. The hormone then shuttles glucose from your blood into your muscle and fat cells, where it can be used for energy or stored for later use. Thereby lowering and stabilizing your blood glucose levels.
So, when your body is functioning optimally, blood glucose and insulin are in lockstep. You eat a meal, blood glucose level goes up, insulin goes up, blood glucose level goes down, and insulin goes down.
So, how does insulin (supposedly) cause weight gain?
With everything we’ve covered till far, insulin sounds like a ‘good guy.’ Without it, glucose would build up in the blood. Having too much sugar in the blood for prolonged periods (i.e. hyperglycemia) can damage the vessels that supply blood to vital organs, which can increase the risk of heart disease and stroke, kidney disease, vision problems, and nerve problems. Eeks. So, what’s up with all the bad rep insulin gets? It really has to do with two other roles insulin plays in your body.
#1: Insulin inhibits lipolysis
During lipolysis, your body breaks down the fat in your adipose tissue stores — fatty tissues that cushion and line your bodies and organs — into free-moving fatty acids that can be repurposed or used as fuel. Interestingly, high insulin levels inhibit this process. Thus, explaining why many people equate insulin spikes with ‘turning off’ your body’s ability to burn fat. Misguided thinking, of course, but we’ll get to that in a bit.
#2: Insulin stimulates lipogenesis
Just so you know, lipogenesis is the process your body uses to move fatty acids from your bloodstream into your adipose tissue stores, where they’re stored for later use. If it makes things a little easier, you can think of lipogenesis as the ‘fat storage mode.’ It’s kind of the opposite of lipolysis. Also worthy of mention is the fact that your body can also convert and store carbs as fat through a process known as de novo lipogenesis (DNL). That said, it’s crucial to note that DNL only happens in meaningful amounts when you consistently eat in a calorie- and carb- surplus.
Wait a minute — when you take into account these two roles of insulin, you’d almost feel compelled to conclude that insulin is indeed the culprit behind weight gain. Not only does it inhibit lipolysis (i.e. prevent the breaking down of fats), but it also stimulates lipogenesis (i.e. triggers the storing of fat)! At first glance, it definitely seems as though insulin is the villain here. But this view is too simplistic and naïve.
Attributing weight gain to a single hormone is too simplistic
Instead of thinking that insulin’s primary purpose is to make you fat, you should think of it as a hormone that helps your body use and absorb the food you’ve eaten in the best way possible. Think about it: why would your body want to break down more fat when there’s already plenty of incoming, readily-available nutrients from your meal (e.g. carbs and protein)? Insulin here is just doing the sensible and rational thing to keep you alive. Consider this: if you had plenty of takeaway food stored in your fridge, would you still cook dinner? Probably not.
And perhaps more importantly, insulin isn’t the only hormone in your body. There’s always a complex interplay of various hormones and enzymes that control your body’s response to a meal. For instance, while insulin inhibits fat-burning, other hormones that are active — such as glucagon, growth hormone, cortisol, and epinephrine — stimulate fat-burning. And while insulin stimulates fat storage, other hormones, such as leptin, inhibit fat storage.
So, to say that insulin is the sole hormone responsible for weight gain when there are so many other hormones and enzymes in your body is too myopic. It’s akin to saying that the cause of extreme poverty is that of individuals not working hard enough, instead of taking into account other crucial factors such as lack of education, poor healthcare systems, lack of government support, etc.
Back to the issue on hand — the takeaway from this section should be that when your insulin levels are high, you’ll burn less fat than when your insulin levels are low. But your body’s fat-burning engines won’t shut off completely, as had been suggested by so many ‘health experts’ and ‘fitness gurus’ (who often have a low-carb cookbook to sell).
More proof why you shouldn’t blame insulin for your weight gain
OK, I hear people saying, “So what if there are other hormones at play? I still believe that insulin is the Bad Guy. I controlled my insulin levels and dropped 30 pounds. How about that?” Well, the following points might help.
#1: Protein is a potent stimulator of insulin too
This is a fact carbohydrate-insulin model proponents and insulin-haters like to avoid. Truth is, protein is a potent stimulator of insulin too. In fact, high-protein, low-carbohydrate (HPLC) meals can cause more insulin to be released than high-carbohydrate meals. Your body releases as much insulin when you eat beef as when you eat brown rice. And more importantly, protein also causes a rapid rise in insulin followed by a rapid decline — just like carbs.
And yet (here’s the important bit), high-protein diets have consistently been shown to be effective at aiding in and maintaining weight loss. Surprised? Besides, here’s something fun to think about. As per the beliefs of insulin-haters, if the elimination of insulin spikes leads to fat loss, what macronutrient are they left with to eat? Carbs are definitely out of the picture. So is protein. I don’t know about you, but I’d pay to see what they’d eat.
#2: Low-carb diets do not lead to greater weight loss results
Even if we were to overlook the fact highlighted above (i.e. that protein also causes insulin spikes, yet is effective in weight loss), this upcoming point is probably going to drive the nail into the coffin for the theory that insulin causes weight gain. And that is, low-carb, high-fat (LCHF) diets do not produce greater weight loss compared to high-carb, low-fat (HCLF) diets when protein and calories are equated. To quote a recent meta-analysis:
When total calories and protein are equated, the amount of carbohydrates versus fats does not produce differences in fat loss.
In fact, high-carb, low-fat diets actually produced a slight advantage in energy expenditure and fat loss.
#3: Insulin does not make you hungry
Also, remember how the carbohydrate-insulin model proposes that because insulin drives all nutrients to be stored as fat, the body essentially ‘starves,’ forcing you to eat more? Here’s the thing. The evidence to support this assertion is extremely weak. If insulin were to really be responsible for ‘emptying’ your bloodstream of fatty acids and glucose (by storing them), then you’d expect that obese people and diabetics — individuals with elevated levels of insulin — would have lower levels of circulating fatty acids, right? Research shows this is not the case. People with obesity actually exhibit normal or even high levels of fatty acids in their bloodstream. Not to mention, insulin has consistently been shown to suppress appetite, instead of stimulating it.
Insulin is not the villain
Truth is, insulin is not the terrible fat-gaining hormone that self-made fitness and nutrition gurus make it out to be. If you truly wanted to minimize insulin spikes, you’d have to go on a low-carbohydrate, low-protein, and high-fat diet. Imagine what that’s like! Bottom line? Instead of fixating on insulin spikes, focus your attention on staying within a calorie deficit (i.e. eating fewer calories than your body burns). Because that’s the key to losing weight. That said, it’s not to say that all you have to care about is the number of calories you eat. You can’t just eat 1,600 calories worth of chips every day. You’d lose weight, of course (if you’re in a calorie deficit), but it’s not healthy. So, no — nothing that extreme. You still need to focus on the quality of your calories. For example, your macronutrient and micronutrient requirements.
While this can be hard to hear, it has to be said: there is no ‘best diet.’ A universal, cookie-cutter nutrition plan that works for everyone doesn’t exist. There is only what works best for you — something that allows you to be in a calorie deficit, yet is sustainable, healthy, and enjoyable for you. If it’s intermittent fasting, great. And if it’s the ketogenic diet, sure, why not. Just know that the reasons why these diets work are that they create a calorie deficit, sometimes without you even realizing — it’s not that they’re superior to the traditional way of dieting (i.e. calorie-restriction). And just, please, for the last time, don’t blame your weight gain on insulin.
Thanks for reading! If you want an evidence-based approach to optimizing your nutrition beyond the number of calories you eat daily, I’ve written a comprehensive guide on macronutrients and micronutrients. Be sure to check that out!