The calorie theory vs the insulin theory of overweight and why it matters

Our understanding of why we get fat matters because these two different theories result in different actions for us if we want to loose weight.

The calorie theory is that we get fat because we eat more than we exercise.

Obviously this is true. If you gain weight then you have eaten more energy than you used in running your body and brain and in exercising.

The question is: do the excess calories cause the fatness in a meaningful way.

Or to put it another way. When you ate enough calories why didn’t you feel full and stop eating. What made your body store them as fat instead of just running a bit hotter.

So is the amount of calories we eat and the lack of exercise all the explanation we need or is something important happening behind that?

Advice for overweight people based on this theory

  • Cut back on food. Especially cut back on high density food like fat (9kcal per g vs 4 for protein and carbohydrates). If you get hungry, when you eat the recommended food at the recommended amount (like my gestational diabetes friend eating porridge and fruit for breakfast), then that’s odd and weird, just keep going.
  • All calories are equal. It doesn’t matter if you get your target number of calories from fat or protein or carbohydrates. Sugar is no better or worse than any other food, as long as you stick to the right amount of food and get enough vitamins etc in the other food.
  • Exercise more.

The insulin theory of overweight and obesity.

Insulin causes fat cells to lay down fat. It also prevents us from accessing the fat inside our cells. So while insulin is high you have to burn glucose to survive. If insulin is high but you have no glucose, you are in trouble (also you insulin will start to come down now). If you injected insulin you might hypo, as it can’t go away. If your body produced the insulin you might be hungry, hangry or starving till your insulin levels come down (or you eat carbs), but you probably won’t have any more serious effects.

Insulin is raised by eating carbohydrates. Therefore carbohydrates are uniquely fattening compared to protein and fat.

The higher the GI (the glycaemic index) or the more carbohydrates are processed so that they can be very quickly absorbed into the blood, the more they spike up insulin, the more they are fattening.

The more you snack between meals*, the more your insulin levels are permanently high the more you are laying down fat and also unable to access that fat in case you get hungry and run out of blood glucose.

GI alone isn’t a perfect measure, if you eat very high GI food with fat, that makes it low GI, so chocolate, or nutella contains lots of sugar but are still low GI. Sugar itself actually has a GI that’s not too bad because only half of sugar counts to GI**. So while I wouldn’t call nutella healthy, I’d call it better than drinking the same amount of sugar in coke.

So the insulin theory of overweight suggests that you eat a meal and, due to high insulin, immediately lay some of it down as fat even if you would be doing exercise later. At exercise time your breakfast or lunch is already laid down as fat, if you have a little snack (of carbs) or a coke your insulin levels will be too high to allow you to access that fat, and you will need to eat more.

Advice based on this theory:

  • Cut back on carbohydrates with particular reference to what effect they’ll  have on your insulin levels.
    • Avoid starchy foods, i.e. bread, cereal, white rice, potatos. Even if bread is whole grain, the wheat kernel has still been mashed up to flour and it is still very easily digested.
    • Eat as much fat as you like it won’t raise insulin, so it won’t be fattening and your natural appetite mechanisms will soon have you feeling full. Bear in mind that ‘fat’ does not include donuts or pizza, as they both contain far more easily digestible carbohydrate (white flour) than they contain fat. Though the fat from the cheese/frying will slow down the absorption of that carbohydrate compared to if you just ate a spoonful of flour and sugar.
    • At the very least, enjoy the full fat version of your normal food.
    • Eat as much as you want, as long as you stick to the right type of food.
    • Avoid snacking, stick to three meals a day and consider fasting on a regular or occasional basis. This will get your insulin levels down and allow your body to access your fat stores
  • All calories are not at all equal. Carbohydrate, fat and protein are treated completely differently in your body (for example you can only get very limited amount of energy from protein so if your diet cook book says to eat low carb and low fat, they are just wrong. They probably man low ‘white’ carbs and high ‘green’ carbs). Sugar is different again because it is our only source of fructose, which will sleet into the liver and get converted to fats with unknown effects.
  • If you are on a high fat low carb diet you may well get hungry less often as the fat increases satiety and if your insulin levels are generally low, it’s easier for your body to then dip down into using up your fat stores.
  • Exercise is not directly relevant, except that it does use up glucose in your muscles and allows them to then take up more glucose from your blood. That is good, but you can equally just not eat the glucose in the first place. The choice is yours (of course exercise is generally good, but not that relevant for weight loss).
  • Pay attention to how much of your meal is easily digested carbohydrates (bread, rice sugar), more slow release carbohydrate (all veg which is still ~80% carbohydrate), vs fat or protein. If you have a sandwich, some popcorn chips and a banana for lunch, you will have gotten over 60% of your food as carbs. Our current dietary advice is to eat no more than 30% fat are you even getting that much?

Ways in which we know hormones work in other contexts.

When children grow up, they don’t get taller because they eat more than they exercise, they grow because of growth hormone. No growth hormone (or growth hormone receptor) no growth, no matter what you eat. Too much growth hormone leads to being super tall, cutting down on food and exercising more wouldn’t really stop that.

Women have ~21% body fat vs ~14% body fat for men, this is due to hormones, not because all women eat more than they exercise compared to men.

A friend of mine went on thyroid hormones and put weight on, the weight then came off when they came off the hormones.

OK, but what should I do?

So these two theories of why we get fat really determine what changes we try to make to loose weight (eat less and exercise, vs cutting carbs but eating as much as we want). And we can see that while some changes will match up (eating less overall vs eating less carbs specifically, also everyone agrees on cutting out sugar), some are kind of opposite (cut fat vs embrace fat) so if we have the wrong theory, we’ll have the wrong advice. If the wrong advice is just unworkable, and if someone is told to try something and it just doesn’t work, will they fell that it is their own fault they are fat and they just can’t change things?

So if you’re reading this and have tried one set of advice (eat less?) but are not sure if the other set could work (eating more fat instead of bread, rice, potatoes and pasta??) try it for a month? You should see the effects within that time. See if your GP will test your blood before and after that month too. Even if I’m totally wrong, you can’t do that much damage in a month. So have fun experimenting***.

*This could be more complicated, but the point is what is going on with your insulin levels is more important than  the number of calories.

**New blog post coming soon about why sugar has a quite ok GI (unfortunately sugar still needs to stay as an occasional treat).

***I have a whole blog post in my head based on John Kay’s book on why the rich countries are rich: disciplined plurality is key. Plurality means trying a different things, disciplined means stopping that thing if it doesn’t work.