How does intermittent fasting affect your health?

Fasting and/or intermittent fasting has gotten a lot of attention much like many other dietary trends. Especially in the past 15-20 years, many doctors prescribe intermittent fasting to their patients to help them lose weight and, hopefully, reduce their co-morbidities and risk factors associated with excess weight. While this may be a short-term effective way to lose weight, it is not at all what the proponents make it to be.

Didn’t our ancestors fast from time to time?

Yes, but that was not by choice. It was due to food scarcity because they had to hunt and gather food. So if they did not have a successful day or week of hunting, they were forced to fast. If they had access to food, they never chose to fast.

Our bodies are not designed to function well without fuel, much like an automobile, and aircraft, or a train, does not function, or go far without fuel.  

More importantly, when you deprive the body of essential nutrients like amino acids from protein, you are forcing your body to break down muscle tissue to compensate for the lack of amino acids you are not getting from food.

Our brain relies heavily on glucose which is the main source of nutrient that is delivered by your red blood cells. However, our body needs a balance mix of nutrients; protein, carbohydrates and fats, breaks those down into glucose, which is the only way our red blood cells can deliver energy to the rest of the body.

Is fasting safe?

Numerous studies have been conducted on the safety of fasting but they all study different aspects of fasting so it is impossible to know long term safety of fasting related to any given health issue. While at the surface, fasting seems safe, there are many health concerns associated with long term fasting.

• Thyroid Function. One of the main reasons for intermittent fasting is to restrict calories and it succeeds at that. However, that comes at a cost. Thyroid hormone is affected by restricting calories and nutrients, and one of the natural responses to famine is to reduce thyroid hormone release. This will backfire. Some studies have shown that, during the month of Ramadan when Muslims fast as part of a religious ritual, their thyroid hormones are affected. Additionally, the studies showed that fasting causes other metabolic and hormonal changes.
• Altered hormones:
  • Sex hormones in general are affected by fasting, but one of the consequences of fasting on female hormones is irregular menstrual cycle.
  • Female fertility can also be impacted by fasting as female hormones are sensitive to calorie and nutrient restriction.
  • Male hormones can also be affected by fasting and restricting calories. Much like female hormones, male hormones such as Testosterone require amino acids as building blocks of this abundant hormone. ALL hormones are made up of proteins. Long-term fasting may result in lowered testosterone levels.
  • Increased stress hormones: Research shows that fasting increases Cortisol levels, especially in women. Elevated cortisol has many health consequences.
  • Leptin and Ghrelin: 2 important hormones that regulate appetite are affected by fasting. These 2 hormones work in concert to signal hunger when we need to eat and fullness after we are fed. Fasting disrupts the concerted function of these hormones, resulting in loss of hunger cues (Ghrelin), and may cause overeating due to loss of satiety cues (Leptin).
• Risk of Hypoglycemia: Or low blood sugar risk increases as a result of fasting.
• Overall reduction in essential nutrients: The risk of malnutrition is elevated due to restricted eating while fasting, which in turn can result in vitamin deficiencies and other health consequences thereof.
• Sluggish metabolism: Our bodies are designed to shut down metabolism and store fat when food is scarce. This is a natural biological response in order to conserve energy should we be forced to fast because we may not have access to food. Therefore, by fasting, you will essentially push your body to slow down your metabolism and hold onto all the fat to survive. Now, who wants a sluggish metabolism?

In summary, the negative health consequences of fasting or intermittent fasting are far greater than any possible benefits due to calorie restriction. A smarter strategy is to choose calorie poor, nutrient dense foods and a healthy balance of Carbohydrates, Proteins, and fats. The frequency of meals may vary among individuals with different activity levels, age, gender, metabolism, genetics, and even schedules.

For most people, I recommend 4-5 small meals a day, 3-5 hrs apart, to ensure you get sufficient nutrients, good quality calories, and maintain a healthy metabolism.

References:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3401749/

https://www.nature.com/articles/ejcn201332