If you’ve ever attempted to lose weight, chances are you’ve at least been intrigued by the keto diet. Short for “ketogenic,” the diet promises that you’ll lose weight – and especially body fat – based on the insulin-blunting effect of eating a very low-carbohydrate diet.
But it’s not as simple or logical as it seems.
A couple of weeks ago I detailed the unintended consequences of following the Paleo eating plan. Turns out, the keto diet has a few surprises of its own.
The ketogenic diet was first developed to help lessen seizures in children. Powering the brain with ketones instead of glucose reduced seizure frequency. Normally, the carbohydrates we eat are turned into blood sugar or glucose, the primary fuel for the body and brain. When we don't eat enough carbohydrates, our bodies have a back-up system to burn fat instead. The liver can turn stored fat and the fat we eat into fatty acids and ketone bodies for energy. And ketone bodies can power the brain instead of glucose.
This is an adaptive mechanism, ensuring that we won’t become stupid if we skip breakfast. In fact, any form of near-starvation will trigger this metabolic change so our brains continue receiving fuel.
Keto enthusiasts take things several steps further. They surmise that because insulin is a storage hormone, lowering insulin levels should improve blood sugar control, cholesterol levels and reduce fat stores. And how do you ensure your insulin levels are super low? By eating mostly fat instead of carbohydrates.
A typical keto plan calls for just 5 percent of calories from carbs, 15 percent from protein and a whopping 80 percent from fat. (Talk about butter being back!) For comparison, individuals living in Blue Zones - those communities around the globe where people experience exceptional healthy longevity - get 65 percent of their calories from carbohydrates. Apparently keto advocates would tell you that all those centenarians are just plain wrong.
In terms of fat stores, the keto theory seems suspect from the get go. After all, how can you lose net body fat if you’re purposefully taking in high levels of it? The short answer: You can’t. Keto diets may cause you to lose weight, but objective studies show that fat stores don’t change much. Most of the weight loss is water and protein. This helps explain why leg muscles of CrossFit participants placed on a ketogenic diet shrink by as much as 8 percent.
And the cholesterol and blood sugar bit? Blood sugars may go down – after all, you’re severely restricting carbohydrates, the main source of circulating glucose. But the diet isn’t great for cholesterol: Studies have shown as much as 35% average increases in LDL cholesterol in participants on the keto plan. In my practice, I have personally witnessed a surge in patients with high cholesterol who have adopted this eating pattern.
High cholesterol, preserved body fat and lost muscle mass: not exactly the trade-off you’d want for a few lost pounds. Apparently, those Blue Zone centenarians have had it right all along.