Physiology, Fasting (2023)

FAQs

What are physiological benefits of fasting? ›

Fasting has been associated with several health benefits, including weight loss, improved blood sugar control, decreased inflammation, and enhanced heart health. It might also offer protection against certain conditions like cancer and neurodegenerative disorders.

Most glycogen is stored in the liver, which has the greatest role in the maintenance of blood glucose during the first 24 hours of a fast. After fasting for around 24 hours, glycogen stores are depleted causing the body to utilize energy stores from adipose tissue and protein stores.

There are three main types of fasts: calorie restriction, nutrient restriction, and seasonal eating.

The four phases include the fed state, early fasting state, fasting state, and long-term fasting state (starvation state). Each phase varies based on the primary source of energy used for the body, as well as how it affects your metabolism and levels of specific hormones.

Many medical experts agree that a one-day fast can feel great, but extending beyond three days can begin to be harmful, especially if you have other medical conditions, such as diabetes or heart disease. “A fast longer than a day or two can deplete vitamins, minerals and electrolytes,” Dr. Hopkins says.

The 5 Stages of Intermittent Fasting with the LIFE Fasting Tracker app: 1) Ketosis and heavy ketosis, 2) Autophagy, 3) Growth hormone, 4) Insulin reduction, 5) Immune cell rejuvenation!

The liver takes up glucose and synthesizes glycogen and triglycerides following food intake, releases glucose produced by glycogenolysis or gluconeogenesis and triggers ketogenesis during fasting (23).

As blood glucose levels fall during fasting, the pancreas secretes increased amounts of glucagon. This action also reduces insulin secretion, which in turn decreases glucose storage in the form of glycogen.

To give you a rule of thumb: after approximately 80 minutes of exercise at a maximum lactate steady state, glycogen stores are depleted.

Likely, the best method to fast is a 3-day fast every month or every new season. Be cautious with fasting under certain conditions, including if you are too thin, malnourished, are under 18, have a chronic disease, or are pregnant or breastfeeding.

What is the healthiest fasting? ›

One study reports that alternate day fasting is effective for weight loss and heart health in both healthy and overweight adults. The researchers found that the 32 participants lost an average of 5.2 kilograms (kg), or just over 11 pounds (lb), over a 12-week period.

Dirty fasting is a term used to describe consuming some calories during a fasting window. This differs from traditional fasting or “clean” fasting, which restricts all foods and calorie-containing beverages. People who practice dirty fasting will typically consume up to 100 calories during their fasting window.

A key sign of autophagy is reduced appetite. It's likely due to changed levels of hormones like glucagon and insulin. Specifically, levels of glucagon tend to increase during autophagy. Glucagon helps manage your blood sugar levels and has been shown to suppress appetite ( 6 , 10 , 11 ).

The 72-h fasting induced significant decreases in glucose level, body weight, and an increase of ketone bodies that confirmed successful fasting of the volunteers. In addition, the median of BDI-2 increased significantly (4 vs. 7, p = 0.006).

The truth about lemon water and intermittent fasting

Long story short - the answer to the question “Does lemon water break a fast?” is no, lemon water does not break a fast. Lemon water contains almost no calories and zero sugars, it doesn't raise insulin levels, which means it will not break your fast (1).

Larance Lab research

“We know that fasting can be an effective intervention to treat disease and improve liver health.

A new scientific study has backed up some health claims about eating less. The clinical trial reveals that cutting back on food for just 5 days a month could help prevent or treat age-related illnesses like diabetes and cardiovascular disease.

Usually, fasting doesn't cause diarrhea on its own. In fact, you're more likely to get diarrhea from breaking your fast than you are while performing the fast. That's because your bowel's ability to function properly decreases when it's not used.

Longer periods without food, such as 24, 36, 48 and 72-hour fasting periods, are not necessarily better for you and may be dangerous. Going too long without eating might actually encourage your body to start storing more fat in response to starvation.

The short answer is yes, you can drink coffee while intermittent fasting. But, this answer comes with a big caveat: You can drink black coffee while intermittent fasting, but coffee drinks with cream, sugar, or other forms of calories technically break your fast.

Does fasting burn belly fat? ›

Intermittent fasting is a convenient way to lose weight without counting calories. Many studies show that it can help you lose weight and belly fat.

Yes, it is possible to lose calories, fat and weight from this popular diet. However, it is also possible to quickly gain the weight back, develop low energy stores which can result in a depressed mood, have problems sleeping and even develop organ damage if the fasting is extreme.

None of the six included studies were confounded by exercise or other interventions. Therefore, intermittent fasting has an independent and significant benefit on weight loss and improvement of liver function in patients with NAFLD.

A 2013 study concluded that fasting for more than 24 hours may lower inflammation by reducing oxidative stress in cells. A 2014 study found that both intermittent fasting and alternate-day fasting were as effective as limiting calorie intake at reducing insulin resistance.

To accomplish the 24-hour fast, you would continue fasting until dinner the following day. This resets the metabolism every time. It works because of the effect it has on two hormones, insulin and growth hormone. When in the non-fed state, insulin goes down which allows the body to access and utilize fat as fuel.

Intermittent Fasting can also help balance hormones, confirms James Roche, “There is substantial research that suggests that intermittent fasting may help to improve hormonal balance. This can enhance metabolism and sleep, leave us feeling more energized and also help us to more effectively burn more calories.”

Animal studies suggest that fasting protects brain cells by providing ketones for fuel instead of glucose. Ketones appear to help the brain produce brain-derived neurotrophic factor (BDNF), a compound that promotes the growth of new brain cells and new connections between them.

If you are going to try glycogen depletion workouts, the best time to do them is during long runs because your body will naturally run out of glycogen after 90 minutes or so.

Once all the stored glycogen is depleted, you will feel tired, fatigued, and your exercise performance will suffer. The glycogen that is stored in our muscles is for “locals only.” In other words, once it's stored in muscle, it's not capable of being transported to other areas of the body to provide fuel.

In a high-intensity workout, although your body uses your glycogen stores first for 'fast energy', it depletes the glycogen stores rapidly enough to force your body to tap on the fat storage. This means that high-intensity workouts are more efficient in burning way more total calories – both glycogen and fat calories.

What fat burns first when fasting? ›

You will first lose hard fat that surrounds your organs like liver, kidneys and then you will start to lose soft fat like waistline and thigh fat. The fat loss from around the organs makes you leaner and stronger.

Occasional fasting combined with regular weight training is best for fat loss, Pilon says. By going on one or two 24-hour fasts during the week, you allow yourself to eat a slightly higher number of calories on the other five or six nonfasting days.

The fountain of youth may be a myth, but you can turn to the next best option: the anti-aging impact of intermittent fasting. Intermittent fasting triggers multiple changes in your body that slow down aging by keeping cells and DNA healthy.

Does sleeping count as fasting? A. Yes, while following intermittent fasting, sleeping is considered a fasting period. Therefore, one does not consume food or drinks during this state.

Most of these regimens advise short fast periods of 8–24 hours. However, some people choose to undertake much longer fasts of 48 and even up to 72 hours. Longer fast periods increase your risk of problems associated with fasting.

As part of a 2019 study, researchers followed 19 adults with metabolic syndrome whose meals were spread over a 14-hour window and found limiting meals to a 10-hour window (followed by 14 hours of fasting) was associated with weight loss, smaller waist circumference, lower blood pressure and LDL “bad” cholesterol.

Other foods allowed during fasting are vegetables, whether fermented or unfermented, sauerkraut, tempeh, lettuce, celery, tomatoes, strawberries, cucumber, skimmed milk, and plain yoghurts. You should also make sure to drink lots of water during this period.

Gum contains calories

For stricter forms of fasting like water fasts, consuming any calories technically breaks your fast. This is especially true if you're chewing multiple sticks of gum per day or choosing a type of gum that's high in sugar.

The Effect of Short-Term Fasting on Human Psychological Health. Some studies reported that short-term fasting can increase negative emotions (depression, anxiety, anger, irritability, fatigue, and tension) and decrease positive emotions and vitality [25–29].

Does fasting have scientific benefits? ›

Fasting has been shown to improve biomarkers of disease, reduce oxidative stress and preserve learning and memory functioning, according to Mark Mattson, senior investigator for the National Institute on Aging, part of the US National Institutes of Health.

There is no set time that water fasting should last for, but medical advice generally suggests anywhere from 24 hours to 3 days as the maximum time to go without food.

A 2021 systematic review and meta-analysis out of Frontiers In Nutrition found that intermittent fasting could reduce liver enzyme levels (ALT,AST) in people living with fatty liver disease.

Studies have shown that extended fasting, such as water fasting for a week or more, can result in positive effects like weight loss, body fat loss, reduced levels of perceived stress, increased ketogenesis, and decreased blood sugar levels.

Likely, the best method to fast is a 3-day fast every month or every new season. Be cautious with fasting under certain conditions, including if you are too thin, malnourished, are under 18, have a chronic disease, or are pregnant or breastfeeding.

After eight hours without eating, your body will begin to use stored fats for energy. Your body will continue to use stored fat to create energy throughout the remainder of your 24-hour fast. Fasts that last longer than 24 hours may lead to your body to start converting stored proteins into energy.

Animal studies suggest that fasting protects brain cells by providing ketones for fuel instead of glucose. Ketones appear to help the brain produce brain-derived neurotrophic factor (BDNF), a compound that promotes the growth of new brain cells and new connections between them.

Can fasting help with depression? Some researchers believe that fasting can help reduce certain mental health issues, including depression. For example, a 2021 review reported that people who fasted had lower anxiety and depression scores than control groups who did not fast.

The liver helps by converting non-carbohydrate materials like lactate, amino acids, and fats into glucose energy. Because our bodies conserve energy during fasting, our basal metabolic rate (the amount of energy our bodies burn while resting) becomes more efficient, thereby lowering our heart rate and blood pressure.

Fasting for 48 hours may boost your health by promoting weight loss, improving insulin sensitivity, and reducing inflammation. It may also help you live longer by delaying cell aging.

What happens after 24 hours of fasting? ›

Once you pass 24 hours of fasting, your body will enter into a state called ketosis, where you're reliant on burning your fat stores for energy. As fat cells are broken down for energy, ketone bodies are created and released into the bloodstream. Ketone bodies act as fuel for the brain when glucose is scarce.