Intermittent fasting (IF) is everywhere right now, although the definition varies. Recommendations include fasting for 16 hours a day, 20 hours a day, all day every other day, every third day, twice a week, once a week, once every other week or just when you’re not hungry.
Here’s my take on IF: the use of sporadic eating patterns to lose fat can be effective, but it isn’t healthy, sustainable or beneficial. Here’s why.
When you don’t supply the body with protein every few hours, muscle degradation occurs. Some will argue you can maintain muscle with an intermittent eating pattern, but I’m interested in promoting optimal muscle mass for health and performance.
Research shows increasing muscle mass requires stimuli including weight training, amino acids, testosterone and growth hormone. A study of active but non-weight-trained men on a calorie-restricted diet that provided a robust 1.5g protein per kilo of bodyweight a day resulted in a 20% reduction of protein synthesis after ten days. The effect was a 1kg loss of lean muscle mass. So failing to eat enough during the 24 hours after weight training results in significantly lower protein synthesis and slower recovery.
At first, reports suggested IF enhances alertness, brain function and, possibly, insulin health in men. But the long-term effects, especially for lean men interested in athletic performance, are suboptimal. Why? Irregular eating leads to spikes in insulin and erratic blood sugar levels, which ultimately sends your hormones, neurotransmitters and circadian rhythm – your internal body clock – out of whack (see below for how else this affects you).
One study tested how IF during Ramadan affected performance and fatigue in elite judo athletes. Results showed that daylight fasting led to a significant increase in fatigue, a slight decrease in power output and anaerobic performance, and a loss of 1.8% body mass. In contrast, eating a typical paleo meal of high protein, low carbs and healthy fats every few hours provides your body with a steady source of amino acids for muscle building and improves cognition and metabolism.
Poor insulin response
Irregular eating patterns influence insulin and blood sugar health. One study analysed insulin and glucose levels over three days in two diet models: intermittent fasting and eating meals five times a day using 55% carbs, 30% fat and 15% protein. The IF model produced significantly greater spikes and troughs of insulin and glucose, indicating a biological milieu primed for insulin resistance, a precursor of diabetes.
Limiting high-glycaemic carbs is the key to insulin and blood sugar health. A study that compared three daily meal plans – three high-carb meals, six high-carb meals and six high-protein, low-carb meals – found that blood sugar was highest in response to the six high-carb meals, followed by the three high-carb meals, with insulin the same in both. The high-protein meals produced dramatically lower insulin and glucose levels. So, for insulin health focus on what you eat – protein, good fats, and low-glycaemic carbs – rather than when you eat.
The effect of IF on hormones is devastating. Levels of metabolic hormones (insulin), anabolic hormones (testosterone and growth hormone) and energising hormones of the adrenal glands are related, so when one hormone-producing gland goes awry you can bet the others will be negatively affected. This can result in poor metabolism and body composition, inability to build muscle, infertility, chronic fatigue, sleep disorders, inflammation and increased risk of disease.
In an indicative eight-week study, middle-aged people went on a diet of either one meal a day or three meals a day with unrestricted calories. The first group lost 2kg fat more than the second group on average. However, they also experienced a significant increase in blood pressure, which is indicative of altered circadian rhythms.
So, while IF can produce fat loss, it isn’t the best method. In fact, it puts your body’s ability to regulate itself at risk, leading to exhaustion and disease.
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One of the world's premier strength coaches, Charles Poliquin has successfully trained professional athletes and Olympians worldwide. Poliquin writes a monthly column for Men's Fitness about how to train as effectively as possible.