In my previous article, I wrote about what intermittent fasting (IF) is, the different types of fasting, and what the science says about fasting and weight loss.
Today, we continue to discuss other health claims linked to IF, safety concerns and considerations to help you decide for yourself if you should be following this type of eating pattern.
Health claims linked to intermittent fasting
Other than endorsements from health enthusiasts and famous individuals, what makes IF popular in recent times is because it does not require any calorie counting or restriction on the type of food to eat, making it highly adaptable to busy schedules and lifestyles.
What makes it fascinating to researchers and the scientific world is the growing number of research that links it to longevity, sharper mind, and decreased incidences of diseases including cancer and obesity (de Cabo & Mattson, 2020).
Whether or not IF has any unique benefits over other traditional calorie-restricted diets is still currently actively debatable.
Although preliminary evidence suggests that IF could offer metabolic advantage in improving health markers, these need to be supported by further research in humans as the body of evidence on human studies is still relatively small (Ganesan, Habboush, & Sultan, 2018; Mattson, Longo, & Harvie, 2016).
Physiologically, it has long been known that in general, restricting calories in animal studies have been shown to increase lifespan, slow down ageing and improve tolerance to various metabolic stresses in the body. However, the evidence is less convincing in human studies.
At the cellular level, IF in animal and some human studies seem to show benefits such as cell resistance to oxidative and metabolic stresses, activation of antioxidant defence systems, and increased DNA repair, which aids in newer and healthier cells (de Cabo & Mattson, 2020).
Preliminary research found that IF may benefit brain health too. Studies in animals discovered that IF can suppress inflammation in the brain, reducing risks of neurological disorders like stroke, Parkinson’s and Alzheimer’s diseases. Another study found that mice put on brief IF had better memory and learning than non-fasting mice. Other studies found that IF can boost verbal memory in human adults, suggesting potential benefits of IF in thinking and memory (de Cabo & Mattson, 2020).
Proponents of the diet think that the stress from IF triggers immune responses to repair cells and effect positive metabolic changes, i.e. reduction in LDL cholesterol, triglycerides, blood pressure, blood glucose, weight and fat mass (Horne, Muhlestein, & Anderson, 2015; Tinsley & La Bounty, 2015).
There is a valid concern of compensating calories lost during IF and that people might overeat on non-fasting days or during the eating window. However, researchers have mixed findings on this (Horne, Muhlestein, & Anderson, 2015).
Some studies found that IF is beneficial in people with pre-diabetes as fasting for over 12 hours help to keep blood sugar levels low, increase insulin sensitivity, and therefore lowering risk and even improving early stages of diabetes. (Sutton, et al., 2018)
The microbiome living in the human gut appears to have positive effects with IF (Patterson & Sears, 2017). Gastrointestinal functions such as gastric emptying and gastric blood flow following the circadian rhythm are more active in the day. IF prolong non-eating intervals, which can help to reset and regulate the gut microorganisms and its environment, therefore improving human metabolism, gut functions and health (Patterson & Sears, 2017).
Physical and sports performance also seem to improve with IF. For instance, mice fed on alternate-day fasting have better running endurance compared to non-fasting mice. Coordination and balance also improved in those animals that were given some forms of IF regime. A recently published systemic review noted that IF can still help maintain lean mass and help with fat loss when done as part of a resistance training program (Keenan, Cooke, & Belski, 2020).
Research on IF in humans is still at its early stage. More solid work needs to be done before a conclusive recommendation to regard the use of fasting in human health intervention.
What can I eat while intermittent fasting?
There are no rules about what to eat, as IF is about when you eat. Of course for optimal health, healthy weight loss, and prevention of nutrient deficiencies and diseases, eating according to the nutritional guidelines is recommended. This includes nutrient-dense food choices like whole grains, legumes, beans, lean meats, fish, fruits and vegetables making up a large part of the daily diet.
Is intermittent fasting safe?
IF is not recommended for the following groups of people:
- Children and adolescents
- Pregnant and breastfeeding mothers
- Older adults
- Individuals with low body weight (underweight)
- Individuals with a history of eating disorders, or vulnerable to an eating disorder
- People with diabetes on medications that remove glucose from the blood
- Those on medications that require food intake
For generally healthy people, it is safe to follow if you are able to fit the timings into your schedule, and depending on your baseline habits.
Many people like the 16:8 fast as they find it to be the simplest and most sustainable method to stick to. If you intend to do time-restricted fasting like 16:8, and have never gone without food for more than 12 hours (including the time you sleep overnight), then start with 12 hours.
If you have already been going without food or drinks with no-calories for 12 hours, then you may start with 14 hours of fasting. Start slow and increase the fasting hours gradually over time. (e.g. 14 hours fast for 2 weeks, and increase another 30 minutes or 1 hour for 1-2 weeks) This will help you and your body adapts. It is not a race, and 16:8 is not the absolute gold standard for fasting; instead, this is closer to experimenting on what suits you and your lifestyle best.
Experiment on what suits you and your lifestyle best. Learn to be more in tune with your body.
Use this opportunity to be more in tune with your body. You can even progress to 20:4 fast where you fast for 20 hours, and eat for 4 hours. If you find it easy to do, you can advance to one-meal-per-day club where you fast for 23 hours and eat just one meal a day.
However, if you can only tolerate the 14:10 fast, then do what is best for you. Don’t beat yourself for not being able to do an extended fast. Your body will still benefit over the prolonged fasting hours, compared to if you indulge in late-night eating.
If you are unsure if you should start fasting or would like some safety recommendations, it is best to consult with a healthcare or medical professional prior to starting.
IF may have different effects experienced by different people. Some reported side effects are persistent hunger, irritability, low energy, feeling cold, being distracted, and reduced work performance. Drastic ones include irregular or missed periods, insomnia, hair loss, and anxiety. If you experience any of these, it could be a sign to stop IF.
Ensuring adequate hydration is particularly important to mitigate any headaches or constipation. Other downsides related to IF include becoming hyper-focus on food that potentially trigger unhealthy thoughts and behaviours like food-related anxiety, guilt and orthorexia.
Is intermittent fasting for me?
In short, IF is not better or worse than other calorie-restricting diets out there. Some people may have some weight loss success on IF, but others don’t. There is still a lot of research to be done before IF can be recommended as a standard approach for weight loss or other health benefits.
As with all diets, it is also not a one-size-fits-all approach for everyone to follow. Should you decide to try IF, pick a variant you think you can stick with for minimally a few weeks.
If you have decided to try IF, bear in mind that the quality of diet is just as important. It is not possible to binge on unhealthy foods during eating times, and expecting to lose weight and reap health benefits. What matters most is consistency.
de Cabo, R., & Mattson, M. P. (2020). Effects of Intermittent Fasting on Health, Aging, and Disease. The New England Journal of Medicine, 381, 2541-2551. doi:10.1056/NEJMx200002
Ganesan, K., Habboush, Y., & Sultan, S. (2018). Intermittent Fasting: The Choice for a Healthier Lifestyle. Cureus, 10(7), e2947. https://doi.org/10.7759/cureus.2947. Cureus, 10(7), e2947. doi:doi: 10.7759/cureus.2947
Horne, B. D., Muhlestein, J. B., & Anderson, J. L. (2015). Health effects of intermittent fasting: hormesis or harm? A systematic review. The American Journal of Clinical Nutrition, 102(2), 464–470.
Keenan, S., Cooke, M. B., & Belski, R. (2020). The Effects of Intermittent Fasting Combined with Resistance Training on Lean Body Mass: A Systematic Review of Human Studies. Nutrients, 12(8), E2349. doi:https://doi.org/10.3390/nu12082349
Patterson, R. E., & Sears, D. D. (2017). Metabolic effects of intermittent fasting. Annual Review of Nutrition, 37(1), 371-393.
Sutton, E. F., Beyl, R., Early, K. S., Cefalu, W. T., Ravussin, E., & Peterson, C. M. (2018). Early Time-Restricted Feeding Improves Insulin Sensitivity, Blood Pressure, and Oxidative Stress Even without Weight Loss in Men with Prediabetes. Cell Metabolism, 27(6), 1212-1221.e3.
Tinsley, G. M., & La Bounty, P. M. (2015). Effects of intermittent fasting on body composition and clinical health markers in humans. Nutrition Reviews, 73(10), 661-674.