Intermittent fasting is super trendy. Like any diet trend, it’s no surprise that there are drawbacks to the practice that will likely make it a passing fancy in both the fitness and general population. The use of sporadic eating patterns to lose fat can be effective, but that does NOT mean it is healthy, sustainable for the long term, or beneficial for athletes.
Experts and nonexperts in the field of nutrition and fitness recommend a variety of meal frequency or fasting methods—fasting every 16 hours, every 20 hours, 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. The definition of “fasting” varies: In some cases it means eating green vegetables and berries when fasting, in others protein-carb drinks and oatmeal are suggested.
Now, many cultures/religions use fasting as a spiritual practice, however in the animal kingdom, no animal is known to fast voluntarily unless it is ill. In most cases, the same animal will consume plants to induce vomiting.
The research from animal studies on intermittent fasting is in no way conclusive, but trends toward showing that it is generally beneficial for the health of males—reproduction is enhanced—but dangerous for females—they become infertile. For example, female rats “masculinize,” stop menstruating, become hyper alert, and sleep much less. Researchers suggest that when their bodies detect a starvation state they develop traits that will help them find food.
Similar trends are being reported by humans who have tried intermittent fasting. Studies and personal reports by men and women suggest the following cons to the practice:
• Obsession over food during the fast period (watching the clock constantly in expectation of the next meal, which of course raises anxiety).
• An overreliance on coffee that causes severe adrenal fatigue, hormonal, and circadian dysregulation.
• Insomnia, particularly among women, due to activation of the hypocretin neurons that incite wakefulness.
• Hormonal havoc for women takes many forms, including adult acne, metabolic disturbance, obsession over body image, and menstrual irregularities.
• Over time, the ovaries shut down and women stay awake at night, presumably an adaptive response so they can hunt for food to keep them alive. In other words, why become pregnant if you are going to starve the baby?
Here’s my take on the issue. For athletes, anyone interested in building muscle mass, or living a long, energetic life intermittent fasting is not advised for the five following reasons:
#1: Optimal Physical and Cognitive Performance Requires Regular Feedings
The obvious and biggest problem of infrequent feedings is twofold: 1) Acute hormonal disregulation leads to poor energy, focus, and altered homeostasis, and 2) A lack of amino acids in the blood causes a catabolic effect on muscle—this will be covered in #2 below.
Initially, reports suggest that intermittent fasting enhances alertness, brain function, and possibly insulin health, particularly in men. As mentioned above, the effects appear to be negative for women, and the long term effects for men, especially lean men interested in athletic performance, are suboptimal.
Simply, irregular eating leads to spikes in insulin and erratic blood sugar. Ultimately, hormones, neurotransmitters, and circadian rhythms get out of whack. By eating the typical Paleo diet of high-protein, low-carb, healthy fat, one can activate the hypocretin neurons and energetic brain transmitters by feeding the body rather than starving it. This provides a steady source of amino acids for muscle building and improves cognition and metabolism.
By eating a high-protein, low-carb, healthy fat meal every few hours you can stimulate the energizing pathways in the body for superior brain function and energy levels. This enables an even blood sugar, better insulin signaling, and a strong but adaptable homeostasis for longevity.
#2: Protein Synthesis for Building Muscle Requires Protein Feeding
There is a big difference between not losing muscle and putting on muscle. When you don’t supply the body with protein every few hours muscle degradation occurs. Sure, there are everyday folks out there who will argue that you can maintain muscle with an intermittent eating pattern, but I am interested in promoting optimal muscle mass for health and performance. Luckily, there’s piles of research into this issue. A quick glance tells us this:
Positive muscle protein synthesis so that you increase muscle tissue requires various stimuli including amino acids, anabolic hormones, and a high degree of tension from weight training. For example, a 2010 study of active, but unweight-trained men on a calorie-restricted diet that provided a robust dose of 1.5 g/kg/bw of protein a day resulted in a 20 percent reduction of protein synthesis after 10 days. The effect was a 1 kg loss of lean mass.
An example of the benefit of frequent feedings is a study in which trained young men did a lower body workout and then took 80 grams of protein in one of three protein dosing patterns: eight 10-gram doses every 1.5 hours, four 20-gram doses every 3 hours, or two 40-gram doses every 6 hours. The participants who consumed 30 grams of protein every 3 hours had much greater protein synthesis and an increased protein balance than the other two feeding models.
More support for continuous protein feeding is with a recent study that showed how young men who took 40 grams of protein before bedtime increased protein synthesis by 25 percent—a remarkable amount. The men trained in the evening, then took protein at 11:30 pm and protein synthesis was sustained all night.
In comparison, short-term muscle loss with irregular feedings is seen in a 3-day human study in which young men ate twice a day with feedings separated by 12 hours. The men experienced much greater use of muscle protein for energy (called protein oxidation) than a group that ate 5 meals. Researchers strongly caution against using irregular meal frequencies, particularly in older people, because it will accelerate the decline in muscle mass and sarcopenia.
: The balance between protein building and protein loss, which over time would lead to a loss of muscle mass, is amazingly delicate. If you forget or neglect to feed the body in steady doses during the 24-hour period after weight training, you will experience significantly lower protein synthesis and a delayed recovery.
#3: Intermittent Fasting Can Cause Significant Adrenal Stress
The effect of a short-term dietary change and the long-term toll of eating patterns that go against circadian rhythms is radically different. Intermittent fasting sustained for a few weeks or a month probably won’t cause long-term adrenal fatigue, but that doesn’t mean that it’s the BEST way to alter body composition.
The short-term effect on performance is small but significant in a study that tested how Ramadan intermittent fasting affected performance and fatigue in elite judo athletes: Results showed that daylight fasting led to a significant increase in feelings of fatigue, a slight decrease in power output and anaerobic performance, and a loss of 1.8 percent body mass of which 0.65 kg was fat lost.
There are no studies about the long-term effects of erratic eating in athletes, but we can guess based on what we know of overtraining. Long periods without food trigger a rise in the catecholamine hormones. If you experience this day in and day out, it can cause the adrenal glands to fatigue, and eventually shut down. The adrenal hormone receptors become less responsive, leading to chronic exhaustion, reduced central nervous drive, and altered metabolism.
Short-term intermittent fasting will decrease optimal athletic performance. Long-term it may lead to adrenal fatigue and lack of homeostasis in the body.
#4: Insulin Health Is More About What You Eat Than When You Eat
Irregular eating patterns influence insulin and blood sugar health. The research is not conclusive on this issue—men tend to have improved insulin health, women have worse. The obese in both genders tend to improve insulin health, but other factors are affected such as blood pressure, and fasting, just like caloric restriction, is considered unsustainable by many scientists.
However, don’t believe the hype that intermittent fasting necessarily improves insulin sensitivity. One study in the journal PLOS One compared insulin and glucose over 3 days in response to an intermittent fasting model and regular meals 5 times a day using a diet of 55 percent carbs, 30 percent fat and 15 percent protein. Results showed that the intermittent eating model produced significantly greater spikes and troughs of insulin and glucose, indicating a biological milieu primed for insulin resistance over time.
Limiting high-glycemic carbs is the real key to insulin and blood sugar health. A study that compared eating 3 high-carb, 6 high-carb, or 6 high-protein low-carb meals a day found that blood sugar was highest in response to the 6-carb meals, followed by the 3-carb meals, whereas insulin was the same in both carb models. The high-protein meals produced dramatically lower insulin and glucose levels.
For insulin health, focus on what you eat (protein, good fat, low-glycemic carbs) rather than when you eat.
#5: Intermittent Fasting Will Mess Up Hormones & Circadian Rhythms
The effect of intermittent fasting on hormones and circadian rhythms is devastating. First, the entire hormonal cascade (metabolic hormones like insulin, anabolic hormones like testosterone and growth hormone, and energizing hormones of the adrenal glands) is interrelated. When one hormone-producing gland gets out of whack, you can bet that others will be negatively affected. This can produce any of the following: Poor metabolism and body composition, inability to build muscle, infertility, chronic fatigue, sleep disorders, a pro-inflammatory state, and increased risk of disease.
A glimpse of this with intermittent fasting comes from an 8-week study in which middle-aged people went on a 1-meal-a-day diet or a regular 3 meal-a-day diet—calories were not restricted. Results showed that the 1-meal-a-day group diet lost 2 kg of fat compared to the 3-meals-a-day group, however they also had a significant increase in blood pressure. Elevated blood pressure is indicative of altered circadian rhythms.
In addition, cortisol, which was measured in the late afternoon before eating the 1 meal, was 48 percent lower than at baseline. This is further evidence of diurnal dysregulation. Yes, you want to minimize cortisol for health and body composition, but that doesn’t mean you want irregular cortisol, which is a symptom of adrenal fatigue.
Due to how intermittent fasting compromised circadian rhythm and affected cortisol, researchers write that the reduced meal frequency “does not afford major health benefits for humans.”
Intermittent fasting can produce fat loss, but it is NOT the best method. In fact, it puts you at risk of altering your hormones and circadian rhythms. You may compromise your body’s ability to regulate itself, leading to exhaustion and disease. Instead, I suggest the following tips for performance, health, and body composition:
• Eat 5 to 6 meals a day from high-protein, low-carb, healthy fat, whole food sources.
• Eating and hunger should not cause you more stress than not eating. Use the presented evidence to find a meal frequency pattern that works for you.
• Avoid using coffee or stimulants to keep you from eating.
• Honor your food. It’s a privilege to eat well, though eating should not be a reward.
• Eat a variety of foods—see the link to my varied Meat and Nut Breakfast at the end of this article.
• Avoid all processed and refined foods in favor of whole foods.
• Use workout nutrition wisely—see the link to an article at the end.
• Hydrate yourself. Muscle gains correlate with hydration status.
• A cleanse that includes fasting is recommended but out of the scope of this article.
• If you are still considering intermittent fasting and are a female of reproductive age, be aware that sporadic eating does not support fertility and female health. Please do more research before engaging in intermittent fasting.
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