What is Intermittent Fasting?
Intermittent fasting (IF) is a dietary practice that involves alternating periods of fasting and eating. Unlike traditional diets that focus on what you eat in a day, intermittent fasting is more about when you eat. It's not a diet, but rather a lifestyle change that can help you achieve better health outcomes.
How to Do Intermittent Fasting?
There are many different ways to practice intermittent fasting, but the most common methods include the 16/8 method, the 5:2 method, and alternate-day fasting.
The 16/8 method involves eating within an 8-hour window and fasting for the remaining 16 hours. For example, you might eat from noon to 8 p.m. and fast from 8 p.m. to noon the following day.
The 5:2 method involves eating normally for five days and restricting calorie intake to 500-600 calories for the remaining two days.
Alternate-day fasting involves fasting every other day, either by completely abstaining from food or limiting calorie intake to 500-600 calories.
2 large meals per day is another popular approach which allows breakfast between 06:00 a.m. and 10:00 a.m. and lunch between 12:00 p.m. and 04:00 p.m. and no dinner.
Science Behind Intermittent Fasting:
Intermittent fasting has been clinically proven to be an effective method for healthy weight loss. When you fast, your body uses stored fat as a source of energy, which can lead to weight loss. Additionally, intermittent fasting can also improve insulin sensitivity, lower inflammation, and increase levels of human growth hormone, which can lead to increased muscle mass.
What is a Metabolic Switch and How Does It Regulate Weight Loss?
Glucose is the primary source of energy for our body during the day, which comes from the food we eat. After we eat, the body uses glucose for energy and stores excess fat as triglycerides in fat cells. When we fast for a prolonged period, the body converts stored triglycerides into fatty acids and glycerol, which are used for energy. The liver converts fatty acids into ketone bodies, which become a significant source of energy during fasting, especially for the brain.
In our normal eating routine, there are two states: fed and post-absorptive. In intermittent fasting, we go through these states as well as a fasting state. During the fed state, insulin is the primary hormone that helps the body use glucose for fuel. In the fasting state, glucagon is the primary hormone, and the body uses stored glycogen in the liver for energy.
The metabolic switch occurs when the body shifts from using glucose to using fatty acids and ketones for energy. This switch typically occurs after 12 hours of fasting when the liver glycogen stores are depleted. This switch helps the body burn fat and maintain muscle mass.
Intermittent fasting has the potential to improve body composition in overweight individuals by inducing this metabolic switch.
Intermittent Fasting Protocols:
|
Protocol |
Frequency |
Duration |
Additional Considerations |
|
Alternate day |
Every other day |
24 h |
|
|
5:2 |
Two days weekly |
24 h each day |
2 other days involve a very low calorie diet |
|
Time-restricted feeding |
Every day |
14–18 h |
Food is consumed over a 6-h period |
|
B2 regimen |
Everyday |
14 h |
2 large meals per day: breakfast between 06:00 a.m. and 10:00 a.m. and lunch between 12:00 p.m. and 04:00 p.m. and no dinner |
|
Weekly 1 day Fasting |
Once a week |
24 h |
Water-only diet 1 day per week and regular eating on the other 6 days of the week |
Source: Vasim I, Majeed CN, DeBoer MD. Intermittent Fasting and Metabolic Health. Nutrients. 2022 Jan 31;14(3):631.
Intermittent Fasting for Blood Glucose Regulation, Diabetes and Weight Loss
Insulin resistance can develop due to increased adiposity and subsequent chronic inflammation, which can lead to the development of insulin resistance. Intermittent fasting can decrease adiposity and related insulin resistance through reduced caloric intake and metabolic reprogramming.
Another hypothesis is that decreased energy intake due to intermittent fasting, will cause a prolonged decrease in insulin production and increased levels of fuel-sensing enzyme (AMPK), which likely plays a role in the improvements in insulin sensitivity and glucose homeostasis.
One interesting study by Sutton et al. investigated the effects of early time-restricted feeding (eTRF) on insulin sensitivity. The study found that eTRF decreased insulin levels and improved insulin sensitivity and β cell responsiveness, although it did not improve glucose levels. This is consistent with multiple other clinical trials, suggesting that intermittent fasting can improve insulin sensitivity and related metabolic markers.
To conclude, Intermittent fasting is a lifestyle change that involves alternating periods of fasting and eating, with different methods to choose from. Scientific evidence has shown that intermittent fasting can lead to healthy weight loss, improve insulin sensitivity, lower inflammation, and increase muscle mass. Intermittent fasting achieves this through the metabolic switch, which is the shift from using glucose to using fatty acids and ketones for energy. Intermittent fasting has also been shown to improve blood glucose regulation and decrease insulin resistance. Overall, intermittent fasting can be an effective and sustainable approach to improving metabolic health.