Not so fast

Podcast: Fasting Diets: What’s the Skinny?

By: Science Vs



After not eating for a period of time your body runs out of sugars to burn and starts burning more fat for energy. An example in the episode was someone who was burning around 50% fat in normal circumstances went up to 70% after fasting.

To study how much fat is being burned they use a machine that analyzes your breath and the ratio of oxygen to carbon dioxide that you exhale. Fat that’s been burned exits the body through exhaling.

People on fasting diets tend to lose weight. A 5 week study that controlled for calories eaten seems to indicate this isn’t a result of fasting, but that people on these diets tend to eat less calories.

Studies of worms and mice indicate that fasting increases the rate at which cells consume and recycle themselves (called autophagy) and can increase longevity. Studies in humans are mixed and much less conclusive.

Studies in mice indicate that fasting can starve cancer cells (many types of cancer aggressively consume sugar for energy) and make them more susceptible to normal cancer treatments. Studies in humans for this are ongoing.


Hungry Hungry Hormones.

Video: The Real Reason It’s So Hard to Lose Weight

By: SciShow



There are mechanisms in the body that push back against weight loss.

When you lose weight, your fat cells produce less leptin. Having less leptin causes your hypothalamus to interpret this as starvation and it increases your desire to eat more and have your body run more efficiently.

Ghrelin levels (signaling hunger) rise and Amylin levels (signaling fullness) go down. The result is the brain increases your appetite.

The brain responds to these changes by making the act of eating feel more pleasurable and rewarding.

Restricting calories causes muscles to rely more on glucose from the food you’re consuming for energy than from the stored fat. They also become more efficient.

Many of these hormones don’t return to normal levels when you stop calorie restricting. They can stay altered for years. Even regaining the weight don’t shift the body out of this mode. Dieting can permanently decrease your resting metabolic rate even if you gain the weight again.

How much energy you use at any point in your life actually varies depending on if you’ve ever been heavier or skinnier.

Thoughts: From an evolutionary standpoint, this is all amazing. The fact that our body can detect a caloric reduction and respond by making everything run more efficiently is an amazing adaptation. And for many people in the modern world this is still a lifesaving mechanism. But for the people in the world with easy access to Coca-Cola and McDonald’s its making it harder to stay at a healthy weight. Technological progress is outpacing evolution.