Contrary to popular belief, fasting for up to four days actually increases your basal metabolic rate. Instead of shutting down to conserve energy, your body activates a hormonal 'fight-or-flight' response that increases energy expenditure to help you find food.
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When training for a mental sport like chess, the foundational step is stabilizing energy by managing glucose metabolism, perhaps via intermittent fasting. Many athletes jump to "smart drugs" and stimulants, but this is ineffective if the underlying energy system is volatile and prone to crashes.
As we age, the timing of calorie consumption becomes more critical than the quantity. One calorie consumed after 6 PM can have the metabolic impact of ten calories consumed before noon due to its effect on insulin production during sleep. This highlights the importance of front-loading caloric intake.
Ferriss notes significant physiological changes while in ketosis, including needing 2-3 fewer hours of sleep and at least doubling his breath-hold time. He also experiences a dramatic reduction in ruminative thoughts, improving mental clarity and sleep onset.
Even if you're not hungry in the morning, eating a substantial breakfast with protein and carbohydrates sets your metabolic tone for the day. This practice stabilizes blood sugar, preventing the crashes that lead to mid-day and evening cravings.
Reducing calorie intake triggers a corresponding drop in your basal metabolic rate. Your body simply starts burning fewer calories to match what you're eating, which stalls weight loss and explains why "just eat less" is flawed advice.
Unlike simple calorie restriction, intermittent fasting lowers insulin levels. This hormonal signal allows your body to access and burn its fat stores to make up for a caloric deficit, preventing the metabolic slowdown that typically sabotages diets.
Eating high-carb foods frequently, even in a calorie deficit, keeps insulin high. This prevents your body from accessing stored fat for energy, forcing it to lower its metabolic rate. After the diet, this suppressed metabolism causes rapid weight regain.
The principle of hormesis shows that stressors like fasting and cold exposure trigger a self-preservation state in cells. This "hunker down" mode activates repair mechanisms like sirtuin proteins, which clean up cellular damage, making these seemingly negative activities profoundly healthy.
Research on "The Biggest Loser" contestants revealed that metabolic slowdown is a response to significant calorie restriction and exercise. Counterintuitively, those with the largest metabolic slowdown were the most successful at losing weight and keeping it off.
A major pitfall of intermittent fasting is the loss of lean muscle tissue. To counteract this, it must be combined with dedicated resistance training. This combination allows for the metabolic benefits of fasting while signaling the body to retain and even build muscle, which can be tracked through strength gains.