This article was previously published on September 4, 2020 and has been updated with new information.
Fasting is a term that describes different approaches to limiting food intake over a 24-hour period or longer. One common approach is occasional fasting, in which people limit the number of hours they eat during the day. There are different approaches to occasional fasting and neither approach is better than the other.
Other people prefer fasting in which they do not eat 24 hours, two or three times a month. Longer posts are possible, but require additional support and knowledge to minimize the negative effects of lack of preparation.
Prolonged food-free times were probably normal for human ancestors who did not have access to a refrigerator or restaurants on every corner. Occasional fasting is more of a lifestyle than a diet, but ultimately, it is a diet that has a significant impact on your metabolism and health.
Fasting actively stimulates metabolism
In a study published in Nature, the researchers found data from participants who underwent a 58-hour fast. A team from the Okinawa Institute of Science and Technology Graduate University in Japan assessed the effects of fasting by analyzing participants ’blood starting at 10 a.m. and ending at 58 a.m. after fasting.1
During the fasting state, the body switches from burning glucose to burning fat for energy, thus producing ketones. Other well-known by-products include butyrates, acylcarnitines and branched chain amino acids.2 Four volunteers signed up for the 58-hour fast, and blood was drawn at 10, 34 and 58 hours.
Some of the compounds peaked at 34 hours, while others were not yet on the plateau at the end of the 58th hour of fasting. A total of 44 substances were identified that changed during the fasting period. In previous studies, researchers have identified only 14.
In addition, none of the participants were threatened, as this is known to change markers during fasting. The researchers identified two butyrates that were “almost invisible” at the 10-hour limit, but reached “big peaks after 34 and 58 hours of fasting”.3 Butyrates help maintain intestinal homeostasis by protecting the intestinal barrier and mucosal immunity.4
The researchers also identified compounds associated with the tricarboxylic acid (TCA) cycle that “reflect enhanced mitochondrial activity in tissues during fasting”.5 Earlier researchers who studied animals have shown that fasting can prolong life.6 The researchers in this study looked for “unknown health effects in human fasting.”7
Fasting metabolites support antiaging
The three metabolites that decline with age are leucine, isoleucine, and ophthalmic acid. However, testing reveals that starving people have higher levels of these metabolites which can help prolong longevity.8
The data also revealed that pyrimidine and purine metabolism was enhanced during fasting. These substances are vital for gene expression, suggesting that this practice may help reprogram protein cells and promote homeostasis. The metabolism of pyrimidine and purine affects the production of antioxidants, which the researchers found to increase significantly during the 58-hour fast.
They believe the data suggest that antioxidant production may be a marker of fasting that can “stimulate the production of several age-related metabolites, which are abundant in young people but depleted in the elderly.”9 Dr. Takayuki Teruya was the first author to comment:
“We have been researching aging and metabolism for many years and we have decided to look for unknown health effects in human fasting. Contrary to initial expectations, fasting has been shown to be quite active in inducing metabolic activation.
People wonder if human beings can enjoy the effects of preventing metabolic diseases and prolonging life by fasting or calorie restriction, as in animal models. Understanding the metabolic changes caused by fasting is expected to give us the wisdom to stay healthy. “
A low-carb breakfast improves weight loss efforts
The time of day when you eat your meals is as important as occasional fasting. For many, fasting is a way to achieve healthy weight loss that they can maintain. In one study of 70 patients, researchers estimated a difference in a morning meal that had limited carbohydrate intake or had the same number of calories as in a typical Mediterranean-style diet.10
In the group of participants, 58.6% were overweight or obese women, and almost one third had diabetes. The group was randomly assigned to one of two breakfast meals, but the rest of the food in their daily diet was identical.
The average intake was between 1300 and 1500 calories per day. While both groups showed improvements, by the end of the study, those who ate breakfast with limited carbohydrate intake showed an impressive 3.5 pounds (7.7 pounds) higher weight loss compared to the other group.
All participants in the restricted carbohydrate intake group lost at least 5% of their body weight by the end of the study compared with 65.7% of all individuals in the control group.
The researchers found no other improvements in the low-carb breakfast group, including those associated with glycemic outcome. Dr. Dimitrios Tsilingiris presented the findings at a meeting of the European Association for the Study of Diabetes in 2018. Commenting on the results, he said:11
A morning diet with limited carbohydrate intake could offer certain benefits by giving adherence to the rules … and the rapid weight loss seen with this diet could be used to induce longer diets, or be an adjunct to weight maintenance, even although not tested for this.
As such, they could be useful in treating type 2 diabetes associated with obesity. However, these diets often have limited versatility and the availability of low-carbohydrate foods can reduce compliance. Normally, we fast overnight, and in the morning, with breakfast, our insulin rises and then falls again towards lunch.
As insulin drops, fat stores tend to mobilize and act as energy substrates. Theoretically, eliciting a lower insulin response after a low-carbohydrate breakfast should mean that we can prolong low [overnight] a state of insulin and fat mobilization, resulting in a net effect on weight and fat loss. “
Late dinner can increase the risk of diabetes
What you eat and at what time you eat significantly affects your health, especially the risk of obesity and diabetes. A recent study published in the Journal of Clinical Endocrinology and Metabolism was led by a team from Johns Hopkins University.12 The researchers recruited 20 healthy young adults who spent two time periods in a clinical research unit where the researchers structured the meals and sleep time of the participants.
The goal was to analyze the metabolic impact of late dinner. In one time period, participants ate a regular dinner at 6 p.m., and in another time period, they ate at 10 p.m. The caloric intake of the meal was the same in both visits.13
The researchers measured insulin, plasma glucose, triglycerides, and oxidation of fatty acids in the diet hourly and in the morning. Participants also underwent a sleep study.
The results showed that eating late in the evening boosted higher glucose levels and reduced fatty acid oxidation. Senior study author Dr. Jonathan Jun said the study:14
“… sheds new light on how late dinner worsens glucose tolerance and reduces the amount of fat burned. If the metabolic effects we noticed during one meal continue to be chronic, then eating late could lead to consequences such as diabetes or obesity.
We still need to do more experiments to see if these effects continue over time and if they are more caused by behaviors (such as sleeping soon after a meal) or circadian rhythms of the body. “
Occasional fasting improves metabolic health
More and more evidence continues to reveal that what you eat and when you eat affects your health. Occasional fasting affects immunometabolism, which is the link between metabolic health and the immune system.15
I believe this is one of the most important areas of emerging medicine and supports what researchers know – metabolic health is key to strong immune function.
In my interview with Dr. Paul Saladino, a certified psychiatrist and nutritionist, we discussed the importance of insulin resistance, which Saladino believes is at the root of many comorbidities responsible for severe COVID-19 disease. The overarching principle is that what matters most to your longevity is your immune and metabolic age, not your biological age.
While the focus of that article was on supporting your metabolic health to reduce your risk of severe COVID-19 disease, realistically, these principles are important in supporting overall good health that protects you from chronic and infectious diseases.
By rejecting the idea of eating three meals a day in favor of trying the occasional fasting approach, you are adjusting to a body that is simply not designed for continuous feeding. When you eat during the day, your body adjusts to using glucose as its primary fuel. This boosts energy storage in the form of fat and increases the risk of becoming progressively more resistant to insulin.
Although many consider occasional fasting a way to lose weight, it also improves insulin resistance, increases human growth hormone production, promotes fat burning, lowers blood pressure and increases mitochondrial energy, efficiency and biosynthesis.
Take control of your health with occasional fasting
While occasional fasting is likely to be beneficial for most people, it is important to remember a few points:
• Occasional fasting does not have to include calorie restriction – Fasting should not cause you to feel weak and lethargic. The goal is to limit the number of hours you eat.
• The craving for sugar will be temporary – As your body begins to burn fat for primary fuel, it will be easier to fast for as long as 18 hours, and your hunger and craving for sugar will disappear.
• Occasional fasting is not recommended with a daily diet of processed foods – While the process may sound like an anti-health remedy, it does not in itself give you all the benefits. The quality of your diet plays a vital role.
If you are new to the idea of occasional fasting, consider starting by skipping breakfast and eating lunch and dinner within the eight-hour time frame. Stop eating three hours before bed. As shown in the aforementioned study, eating before bed can increase your glucose intolerance at night and increase your risk of gaining weight.
Focus on a diet with moderate amounts of healthy protein and reduce your net carbohydrate intake by replacing them with healthy fats such as butter, coconut oil and raw nuts. In general, these strategies can help your body switch to fat burning mode.
It may take a few weeks, after which you will probably be able to fast for 18 hours and you will not feel hungry. By adjusting to a whole food diet and including intermittent fasting, almost every aspect of your health will also begin to improve.