You may have seen articles or social media posts about intermittent fasting. Celebrities and influencers often tout intermittent fasting for weight loss and health improvement.
The practice of fasting is nothing new; it has been practiced for millennia by many people for religious or health reasons. Recent studies have examined the pros and cons of intermittent fasting and you may be wondering if intermittent fasting (IF) is a good choice for you.
The term “intermittent fasting” refers to time-restricted feeding or periods of consuming little to no calories. During a period of fasting, caloric intake can be 0-25% of your daily caloric needs.
Some people don’t eat anything during a period of fasting, while others may only eat a few hundred calories. (1; 2)
There are different types of intermittent fasting schedules. Intermittent fasting can involve fasting for 16 hours, with a window of 8 hours for eating. This is commonly referred to as 16/8 intermittent fasting.
It could mean a 24-hour fast on alternating days. Some people fast for 2 days a week on different, non-consecutive days. For example, they may fast on Monday and Thursday. This is sometimes referred to as the 5/2 intermittent fasting diet. (1)
Other people may have a few days where they only eat a few hundred calories a day. This practice is referred to as the fasting-mimicking diet or reduced-calorie fasting. (3)
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It sometimes seems as if there’s nothing that intermittent fasting can’t help with, and perhaps it’s too good to be true. Recent research has found that there may be some real health benefits of intermittent fasting.
One of the top reasons people try intermittent fasting is for weight loss. Research has confirmed that intermittent fasting may help with losing weight or losing fat.
Studies have shown that IF may help with losing fat and gaining muscle by increasing levels of human growth hormone (HGF). The fasting pattern appears to help promote more human growth hormone in the body naturally, particularly if you fast for 24-48 hours. (4)
If your doctor has told you that you’re prediabetic or have type 2 diabetes, you may be wondering if IF could help you control your blood sugar levels.
Some research has suggested that IF can improve insulin resistance and insulin sensitivity. One study showed insulin-lowering impacts to be greater in an IF group than in a calorie-reduced group. (5)
Another study showed that insulin sensitivity didn’t improve in non-obese individuals but it did in those that were obese. (5) Some studies have found that insulin sensitivity improves with IF through the activation of AMPK, or activated protein kinase, which may influence hunger and fullness cues (6)
For other health concerns, the benefits appear to be linked more with the weight loss that may come with IF.
For example, you may be able to lower your cholesterol levels through the process of weight reduction when following IF.
Studies have found that alternate-day fasting (5/2 intermittent fasting) decreases total cholesterol, LDL cholesterol (low-density lipoprotein, sometimes referred to as “bad cholesterol”), and triglyceride levels. Other studies have found heart health benefits from practicing IF for 6 months in obese and non-obese adults, in addition to obese adolescents. Other studies have also found improvements in systolic blood pressure. (5)
In addition, IF may keep your gut healthy. It seems to improve the diversity and number of healthy gut microbiota, in addition to certain biomarkers that are associated with a healthy gut bacteria balance. (7)
Both healthy and obese subjects were found to have improved diversity in the diversity of microbiota in the gut after practicing 16/8 IF. Furthermore, subjects were found to have more beneficial bacteria strains in the gut after IF. (8)
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While there are certainly some potential benefits with IF, there may also be some downsides. Research has found there to be some negative effects of intermittent fasting.
Frequently reported side effects of fasting include headaches, dizziness, mood swings, lethargy, polyuria, and frequent urination. One study followed 147 individuals practicing IF for 1-3 months and found the most frequent side effects reported were headaches and lethargy. (9)
Other studies have found that practicing IF can increase the risk of hypoglycemia (low blood sugar), low protein and vitamin stores, and dehydration. (5)
People with type 1 diabetes may be particularly susceptible to hypoglycemia or low blood sugar while fasting, so they should exercise caution when fasting. Such individuals should talk with their doctor before starting any sort of fasting pattern. (10)
Women who are pregnant or breastfeeding should be incredibly cautious with any sort of fasting, including IF, as there isn’t sufficient research on the safety of fasting among this population. In addition, children or those under age 18, people with type 1 diabetes, and those with a history of eating disorders may want to avoid intermittent fasting. (11)
As with many diets and dietary patterns, there are benefits and drawbacks to intermittent fasting. If you’re considering IF, you may want to consider some of the mixed data from IF research in comparison to a regular, consistent calorie-reduced diet.
Intermittent fasting may help some individuals with weight loss, but it may not work for everyone. When compared with continuous energy restriction, or a consistent calorie deficit, IF was found to perform about the same in 9 out of 11 studies. (12)
Both intermittent fasting and energy-restricted diets may reduce the inflammatory marker C-reactive protein (CRP), but they don’t impact other inflammatory markers such as TNF-alpha or IL-6. IF may or may not be beneficial for people with chronic inflammatory conditions when compared to an otherwise healthy diet or an anti-inflammatory diet. More research is required. (12)
Intermittent fasting may help with some health markers, but lipids such as high-density lipoprotein (HDL or “good cholesterol”), the ratio of LDL to HDL cholesterol, and other lipid markers have mixed results. Fasting glucose also may not be impacted much by fasting, although there is promise in insulin resistance. (13)
It’s important to remember that fasting can increase the risk of headaches, lethargy, hypoglycemia (low blood sugar), low protein and vitamin stores, and dehydration. (9; 5)
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If you’re considering trying IF, you may be wondering when you can expect to see results. This depends on what health condition you’re targeting through IF.
If you’re trying IF for weight loss, it’s important to note that some studies have found that some modest weight loss results can be seen in as little as 3 weeks, although some studies go up to 24 weeks and beyond. (14; 13)
If you’re trying IF to improve insulin resistance or blood pressure, fasting may also improve these clinical markers in as little as 6 weeks. (13)
Some studies have shown slight decreases in lipid markers such as LDL and triglycerides in 3-52 weeks. (13)
As with all dietary changes, individuals should practice their new eating pattern for several weeks to assess for changes. Many participants choose to continue IF for several years to maintain the health benefits.
After reading about the pros and cons of the intermittent fasting diet, many people wonder how long they can continue fasting while staying safe.
Following the intermittent fasting pattern of 16/8 is generally recognized as safe to do for a long time, even several years. One of the main benefits of the intermittent fasting 16/8 pattern is that it can be done for a long time.
Studies have found that short periods of complete fasting may be safe for 2-3 days. The 5/2 pattern of intermittent fasting discourages taking fast days back-to-back or consecutively. For example, you can fast on a Tuesday and then again on Friday, so you’re not in a fasted state for too long.
For those who follow a fasting-mimicking diet or extremely low calories (around 200-250 calories per day), fasting may be safe for 4- 21 days. (15)
Read more: Green Tea Intermittent Fasting: Benefits and Side Effects
Yes. Fasting is considered to be any amount of time when you’re not eating or drinking calories, whether you’re asleep or awake. The word “breakfast” was originally intended to signal the meal that breaks your fast from the previous night. Generally, research has found a 14:10 or 16:8 pattern of intermittent fasting to yield the best results in reducing belly fat. (16; 17) Some people want to try intermittent fasting as a way of losing weight, shedding belly fat, or improving some health markers, while others like to have more structure to their eating times and may find that they’re more mindful when planning what they will eat during their eating window, thereby making healthier choices.FAQs
Does sleep count as fasting?
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Should you do intermittent fasting?
The practice of fasting is not new, but recent research has confirmed some benefits of fasting for short, set periods. There are some pros and cons to intermittent fasting. If you want to lose weight, improve insulin sensitivity or insulin resistance, or improve cardiovascular health, IF may be beneficial for you. However, people with type 1 diabetes, those with a history of eating disorders, women who are pregnant or breastfeeding, or children shouldn’t try any form of fasting, including intermittent fasting.
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