A tale of two weight loss theories

2015 10 10 14.13.19

In the last century there’ve been two major theories on what makes us fat — the one we grew up with, and one that’s both more recent and, for now at least, more credible.

The old one, that still drives most people’s thinking because it seems so logical, is the calories theory, i.e. too many going in and not enough going out means weight gain.

It follows that the solution is to eat less and exercise more, and fat should be avoided because it contains more calories than protein or carbohydrate. That’s how we ended up with a dietary pyramid that had a base of carbohydrate, protein in the middle, and fats and oils squeezed into the tip.

It’s probably fair to say though that this hasn’t been all that successful, given the growing numbers of us grappling with obesity.

Another flaw in this theory is that it treats all calories as equal, so 100 calories is 100 calories regardless of whether they come from beef, beetroot or bagels. (We use kilojoules in Australia, but calories are easier to talk about.)

Yet foods perform different functions. Protein such as beef, for example, helps with the growth and repair of cells. Beetroot provides minerals, vitamin C and fibre. Bagels, though, provide little more than calories. So to treat them all as equal is off the mark.

Calorie reduction has also led to far too many women missing out on important nutrients by trying to live on rice cakes and other fat-free processed foods, skinless chicken breasts and so on.

The more recent theory is about carbohydrate and insulin.

It’s based on the fact that carbohydrate that quickly breaks down to sugar in our bloodstream (e.g. all those low-fat processed foods) spikes our blood sugar. Insulin is released to bring blood sugar back down by storing it in the muscles and the liver.

But if that stored sugar isn’t used within 24 hours it’s converted to fat.

The body also produces a hormone that does the opposite of insulin, called glucagon. Glucagon breaks down stored fat to be used for fuel.

Insulin and glucagon don’t work at the same time though; if one is in action, the other one isn’t.

Our bodies can use sugar or fat for fuel, but use sugar first. If sugar is available, there’s no need to break down fat. And since glucagon and insulin don’t work at the same time, if insulin is present glucagon gets to rest.

This means that to lose weight we have to eat in such a way that insulin is kept to a minimum and glucagon gets into action.

Another issue with carbohydrate and insulin is that they can trigger food cravings and binge eating.

So while this theory is about what we eat rather than how much, what we eat can influence how much we eat.

The downside of this approach is that there isn’t a ton of research to support its weight loss credentials. Some studies comparing low-fat and low-carb diets have concluded that they produce about the same amount of weight loss (i.e. not that much). Then again, most research on diet and weight is poor.

Still, given it’s a theory that makes good sense, here are a few pointers we can take from it.

1. Any carbohydrate we eat that isn’t used as fuel will be stored as fat, so it works to cut back on those carbs that will spike our blood sugar, especially processed food, junk food, sweet foods, starchy foods like white rice, pasta, bread, potato, most commercial cereals, and so on.

To limit insulin we need to base our meals around foods such as vegetables, meat, fish, eggs, cheese, full-fat yoghurt, berries and healthy fats. Most of us can also manage a few legumes and whole grains such as oats.

And while changing what we eat helps avoid overeating, bear in mind that repeatedly eating too much of anything, no matter how healthy, puts our metabolism in a spin.

In addition, caffeine can encourage the body to make more insulin, so don’t go mad with coffee.


2. Another way to limit insulin is to stick to a maximum of three meals a day, no snacks. The 5:2 diet and intermittent fasting are commonly thought to reduce weight by reducing the number of calories we eat, but it’s likely the explanation is that they reduce insulin.


3. What about glucagon? A good way to mobilise it would be to start your day by exercising on an empty stomach. For example: have dinner, fast overnight, then take Fido for a walk first thing in the morning.

Be mindful though that alcohol can put a spanner in the works. The problem with alcohol is not its caloric content. It’s that the liver has to get rid of the alcohol, and while it’s doing that it stops glucagon from breaking down fat.

So if you want a glass of wine with dinner, eat healthy and eat early. Your liver can get to work offloading the alcohol and you’ll still have some fat burning hours overnight.


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