The Zone Diet: How It Works

The first alternative diet

The first alternative diet we'll take a closer look at is the Zone Diet. It's generally credited to Dr. Barry Sears, author of the bestsellers Enter the Zone and Mastering the Zone, even though diets built on a similar idea had already been described back in the 1970s.

We won't go through every argument Dr. Sears makes for why "conventional" nutrition advice doesn't suit everyone (his discussion of eicosanoids and arachidonic acid, for instance, is a topic on its own). Instead, here's the core idea behind the diet, its fairly simple rules, plus a few practical observations.

Why the Zone?

Dr. Sears uses "the Zone" to describe a state of internal hormonal balance you can reach through your diet. In practice, that mainly means keeping insulin within a fairly tight range — not too high, not too low.

What actually drives insulin, a hormone released by the pancreas? Mainly carbohydrates — and carbs are exactly what conventional nutrition advice tends to encourage eating plenty of. Meanwhile, it turns out that dietary fat on its own doesn't directly drive fat storage nearly as much as you'd expect.

What happens after you eat carbs?

Your digestive system converts any digestible carbohydrate — whether it comes from a sugar cube, rice, or a slice of bread — into glucose. Once that glucose reaches your bloodstream, it triggers insulin release, which brings glucose levels back down (you've probably heard the term "blood sugar" before). Insulin allows glucose into muscle and liver cells, where it's converted into glycogen — the body's stored form of carbohydrate, used to fuel physical activity.

If glycogen stores are already full, which is common in people who aren't very physically active, and there's no immediate energy demand either, the extra glucose gets shuttled into fat cells instead and stored as fat for later use — during fasting, once glycogen is depleted, or during prolonged aerobic activity, for example.

On top of that, insulin's effect doesn't stop the moment blood glucose normalizes — it tends to overshoot, pushing glucose below normal levels. That resulting low blood sugar (hypoglycemia) triggers cravings for more carbohydrate in the brain. That's likely why a plate of pasta at dinner can leave you hungry again just two hours later.

How much your insulin swings varies from person to person — in people who are insulin resistant, even a moderate carb intake can trigger a sharp insulin spike.

So what's the solution?

The right combination of protein, carbohydrate, and fat — one that keeps your insulin "response" within the zone and lets your body convert stored fat into energy, in other words, burn fat. Muscle and brain performance stay high, and the right combination also slows digestion slightly and helps control appetite.

The core idea of the Zone Diet

On the surface it's simple: every meal should be made up of the right ratio of carbohydrate, protein, and fat. That's it. So what's the right ratio? Roughly equal energy from each of the three (with slightly more coming from carbs than from protein or fat). As a percentage of total energy intake, that works out to:

Carbohydrate – 40%, protein – 30%, fat – 30%

You may have also come across this described as the "40-30-30 diet" or the "isocaloric diet" — they're essentially the same idea, differing mainly in opinion on exactly what kind of fat, and how much of it, you should eat (more on that elsewhere).

Since carbs, protein, and fat each provide a different amount of energy per gram, it's more practical to think in terms of a weight ratio instead:

Carbohydrate – 9g, protein – 7g, fat – 3g

In other words, carbohydrate makes up the largest share, protein somewhat less, and fat the smallest share. Dr. Sears calls this combination (9g carb + 7g protein + 3g fat) a "food block," for simplicity.