We say insulin and people think: diabetes. And yes, it’s true that insulin is very important to diabetics because their pancreas no longer makes enough of it (and so they must inject it) but in fact, anybody interested in looking good, feeling good and living longer should educate themselves about how insulin functions in the body.

For those who have been following me on Instagram (@stretch_rayner) you might have seen me measuring my blood glucose levels and ketone level during my KetoDiet experiments.

Why? Well, firstly, your body composition (ie. how much fat and muscle you have) depends on your insulin management. Lots of people think ‘cutting calories’ or ‘going into calorie deficit’ is the best way to lose fat, but are unaware of the resulting hormonal impact, and how eating less affects insulin not only during the calorie deficit but also when they return to eating normally again. Insulin management is one of the keys to achieving both sports performance and body composition goals and most of us have very little idea how to manage it.

So how does insulin work exactly?

The easiest way to think about insulin is to think about a glass of water. If I consistently add more and more sugar into the water and stir it around, it turns into a syrup. This is what happens to our blood if we eat a lot of carbohydrates (sugar). Your heart can’t pump a thick syrup, so the body must move the sugar out of the blood somehow and that’s where insulin comes in. Insulin is released by the pancreas in order to shunt the sugars out of the blood and into either the muscle cells or the fat cells. Oh and, just for the avoidance of doubt… Carbohydrates (CHO) include fruit, vegetables, pasta, rice and bread. All CHO are broken down into glucose by your body once they’re eaten, and your blood sugar level increases after eating these foods. You might also like to know that dairy can raise insulin. Why? Because it contains lactose, which is a type of (yes, you guessed it) sugar! Be aware though, that insulin is not all bad. We use insulin to help manage our blood sugar levels and at times this is helpful. The issue is consistently high levels of insulin.

Why does exercise help with insulin management and help prevent diabetes?

Think of your muscles as little petrol tanks. During exercise, those petrol tanks slowly get emptied. Next time you eat carbohydrates, insulin will push the sugar into the empty muscles (petrol tanks), to fill them up again ready for your next workout. But if you’re not training, the petrol tanks will stay full and the insulin will need to put the sugar somewhere else? Hello, fat cells…

Consistently high sugar levels (high CHO diet) + high insulin levels = an increasing number of fat cells. Worst case scenario? If you keep eating more and more sugar, the pancreas has to keep pumping out more and more insulin and at some stage, it’s going to burn out, much like anything you overuse and abuse. In this case, the pancreas stops being able to produce enough insulin to lower the high blood sugar levels and instead you’ll have to start to inject insulin into the bloodstream – ie. you’re diabetic.

So is fruit much better than refined sugar?

This is a really important point, because whilst fruit obviously has lots of vitamins and nutrients, it can be very high in fructose (grapes are high in fructose for example whereas pineapples are high in another type of sugar called sucrose). Fructose is a special sugar, which is metabolised differently from other sugars – it is metabolised by the liver. If the liver petrol tank is already full of sugar it can’t take anymore, the excess fructose will then get stored as fat on the liver. When this becomes extreme, it can lead to fatty liver disease and increased levels of visceral fat (fat around the vital organs).  High levels of visceral fat are linked to obesity and countless other health issues. In short, for someone who’s exercising regularly 25g of fructose a day is enough (a couple of bananas) whereas someone seeking weight loss shouldn’t eat any more than 20g a day.

A lot of processed foods use corn syrup, fructose syrup, and other crappy syrups to add sweetness.  They proclaim that some of these sweeteners are “healthier” and “diabetic friendly” because many of them don’t raise insulin levels. It’s true, some of them don’t because the fructose is metabolised in the liver and any excess is stored as fat there, the sugar never reaches the blood stream and hence the body does not need to release insulin to manage sugar in the blood. Does this sound healthy to you?  These syrups are everywhere and they are making you fat, start paying more attention to food labels, or simply stop eating processed foods.

Fruit juice is high in fructose and raises insulin levels faster than eating the whole fruit version.  Juice diets are generally a bad idea for those who are looking to improve body composition results as they play havoc with insulin levels.  Most people will lose muscle mass when on a juice diet and then when they start eating normally again they will pile on the fat because less muscle mass means a slower metabolism.

How does insulin as a hormone affect other hormones / bodily processes?

High insulin levels can cause inflammation in the body. If inflammation is generally high, the stress hormone, cortisol, is generally high. If cortisol is high, growth hormone and testosterone will be low. When people eat a lowering carbohydrates diet they reduce their insulin levels and often find inflammation is greatly reduced too (hence they might feel less bloated), and it’s possible to see some pretty dramatic transformations in a short period of time.

This is why weight loss is not as simple as ‘cutting calories’ or ‘going into calorie deficit.’ Our hormones are sensitive to nutritional changes and thus what we eat and drink can significantly impact our hormones, not just insulin.

Calorie-free drinks and insulin

Let’s start with coffee. We know that caffeine in moderation can help enhance workouts. But did you know that coffee can lower your insulin sensitivity (the efficiency with which your body handles incoming sugar)?  Caffeine is a stimulant that increases adrenaline which increases our energy levels partly caused by the increased availability of energy in the form of free fatty acids. This process can lower insulin sensitivity and cause a spike in insulin because sensitivity goes down. It’s best not to eat too many CHO with your coffee, and it's always best to drink coffee before your workouts and not after!  Coffee can help us burn more fat during training if used at the right time. I also don’t recommend drinking coffee on an empty stomach (a post for another time).

And as for Diet Coke (and other ‘diet’ drinks): The problem is when you take in a diet coke, your taste buds taste sweetness and your clever little brain releases insulin in preparation for the sweetness/sugar to come into the bloodstream. But no sugar arrives since there’s none in the Diet Coke? Now you have high insulin levels and low blood sugar levels, i.e. you’re going to crash HARD. You’ll probably also crave carbs, i.e. want something sweet to pick you up. Bottom line: don’t drink this shit. You’re actually better off having the full sugar version (though that’s not to be recommended either – just drink water).

One final thing to think about…

If you’re eating for performance then topping up those petrol tanks is important. But if you’re eating for body composition and you want the body to start burning fat as a fuel source then you want to be eating a low CHO diet. Eating for performance and eating for body composition are two very different things and you need to be clear on your individual goals.