Fasting, or going without food for an extended period of time, has become an increasingly popular health trend in recent years. Proponents of fasting claim that it provides a number of health benefits, including promoting faster healing and recovery from illness or injury. But what does the science say? Here we review the evidence surrounding the effects of fasting on the body’s ability to heal itself.
What happens in the body during fasting?
When you stop eating for an extended period of time, your body goes into a metabolic state called ketosis. This is characterized by the breakdown of fats into ketones, which become the main fuel source for the body and brain in the absence of glucose from food.
Some of the main changes that occur in the body during fasting include:
- Lowered levels of insulin and blood glucose
- Increased lipolysis – breakdown of fat for energy
- Increased levels of growth hormone
- Decreased inflammation
- Increased cellular recycling through autophagy
Many of these effects of fasting are thought to promote healing processes in the body. Lower insulin and blood glucose reduces inflammation, while autophagy clears away damaged cells and recycles their components into nutrients. Growth hormone, which increases during fasting, plays an important role in tissue regeneration.
Does fasting promote faster healing from injury or surgery?
Some research suggests that fasting may help speed up recovery time and healing after surgery or injury.
One study in mice found that a short 3-day fast prior to skin wounds resulted in faster wound healing compared to mice that were fed normally. The fasting mice had increased collagen deposition, improved wound maturation and higher strength recovery in the wound area.
Other animal studies have found improved healing outcomes when fasting before surgical procedures. One study in rats showed that fasting for 3 days sped healing and improved intestinal anastomotic strength after intestinal surgery.
In humans, several clinical studies have also shown benefits. One trial in people undergoing knee surgery found that those assigned to fast for 1 week prior to and 1 week after surgery lost less muscle mass and recovered faster compared to patients who were fed regular meals.
Other studies in patients undergoing gastrointestinal surgery and cardiac procedures also report faster recovery times and reduced complications for those fasting before and/or after surgery.
The benefits are thought to come from the metabolic switching to ketosis and lowering of inflammation that occurs during fasting. However, more high quality clinical trials are still needed to confirm the effect.
Does fasting help the body heal from infections or illness?
The potential healing effects of fasting are not limited to injuries – some evidence also indicates that it may help the body recover from infections and illness.
This may be related to the anti-inflammatory and immune system effects that occur during fasting. When fasting, white blood cell counts initially go down, but immune cell regeneration increases. Human growth hormone also increases, which helps accelerate tissue repair.
Animal research has found intermittent fasting and calorie restriction helps mice better recover from bacterial and viral infections compared to mice fed normal diets.
In humans, preliminary research indicates therapeutic potential for fasting in helping overcome common infections.
One recent 2020 clinical trial in adults found that a 3-day fast followed by a vegetarian diet was safe and effective in helping treat acute respiratory infections. Fasting reduced the duration of symptoms from 8 to 3 days on average versus the control group.
Other preliminary studies report potential benefits for fasting in helping treat asthma, cystic fibrosis and even potentially COVID-19, though more research is needed.
Does fasting help heal gut issues like leaky gut syndrome?
Emerging research suggests fasting may benefit gut health and help heal conditions like leaky gut syndrome. During fasting, gut cells initiate important repair and recycling processes like autophagy. There is also a dramatic change in the gut microbiome.
Some small human trials have shown promise for fasting in improving gut permeability and reducing gut inflammation in patients with autoimmune conditions and irritable bowel syndrome. Inflammatory bowel diseases like Crohn’s disease and ulcerative colitis may also potentially benefit.
One 2015 study had 12 patients with Crohn’s disease follow a “fasting mimicking diet” for 7 days. At the end, they had significantly reduced symptoms, improved quality of life and markers of inflammation.
However, most research is still early stage. More studies are needed to determine if fasting should be recommended for leaky gut and related gastrointestinal disorders.
Can fasting help the body heal from autoimmune conditions?
Some of the most promising research on the healing powers of fasting involve autoimmune diseases. Autoimmune conditions are characterized by an overactive immune system mistakenly attacking healthy tissue.
Animal and some human studies show that fasting could help reset and calm the immune system. Fasting may also limit the release of pro-inflammatory cytokines while increasing anti-inflammatory ones.
One randomized trial in 60 patients with multiple sclerosis split patients into either a fasting group or a regular diet group for 6 months. At the end, the fasting group had significantly less fatigue and fewer symptoms. MRIs showed improvements in brain lesions.
Other preliminary studies show potential benefits for fasting in patients with rheumatoid arthritis, Hashimoto’s thyroiditis and psoriasis.
However, fasting for autoimmune issues is still considered experimental. Anyone with an autoimmune condition should speak to their doctor before attempting a fast.
Can fasting help prevent or treat cancer?
There is some preliminary evidence that fasting could help prevent or even treat certain cancers.
Animal research shows that fasting may help reduce the side effects and increase the effectiveness of chemotherapy drugs. There is also evidence that combining fasting with chemotherapy enhances cancer cell death.
In humans, a few small trials have examined the effects of fasting combined with chemotherapy. Two recent randomized trials in breast cancer and ovarian cancer patients reported improved quality of life and reduced side effects for those who fasted before and after chemo.
Research also shows that fasting for 72 hours can trigger cancer cell death and help protect normal cells. Fasting seems to make cancer cells more vulnerable while protecting healthy cells through stress resistance.
However, much more research is still needed to determine if fasting has potential as a cancer therapy. Patients interested in fasting before, during or after cancer treatment should discuss with their oncology team first.
Is fasting safe? Are there risks or groups who should avoid fasting?
For most healthy individuals, short-term fasting lasting 24-72 hours under medical supervision is considered safe with minimal risks. However, some groups should take precautions or avoid prolonged fasting.
Potential groups who should use caution or avoid fasting include:
- Children and adolescents under 18 – Fasting can impact hormones and growth.
- Underweight individuals – fasting can lead to further weight loss and nutritional deficits.
- Those with gout – fasting can increase uric acid levels and lead to flares.
- Pregnant or breastfeeding women – fasting can be dangerous for both mother and baby.
- Those with type 1 diabetes – fasting can increase the risk of hypoglycemia and ketoacidosis.
- Those with eating disorders or history of disordered eating – fasting may exacerbate the condition.
- Malnourished individuals or those with nutritional deficiencies.
Other side effects that may occur with prolonged fasting include dizziness, headaches, irregular heartbeat and electrolyte imbalances.
Supervision by a doctor who specializes in fasting protocols is recommended to monitor for potential risks and mitigate side effects. Working with a dietitian to ensure proper refeeding after a fast is also advisable.
Should I take supplements while fasting?
During short fasts of 24-72 hours, supplementation is typically not necessary for most healthy adults. The body can draw on its existing vitamin and mineral stores. Consuming only water, herbal tea and saltwater is recommended.
However, for fasting lasting a week or longer, supplementation may help mitigate potential nutrient deficiencies and side effects. Some key supplements to consider include:
- Multivitamin – Provides micronutrients like vitamins B, C, D and minerals like calcium and iron.
- Omega-3 fatty acids – Help regulate inflammation and protect cells.
- Magnesium, potassium and sodium – Important electrolytes.
- Bone broth – Provides protein, collagen and electrolytes.
Introducing supplements should be done carefully during a fast. Start with low doses and increase slowly while monitoring for tolerance. Some supplements like magnesium may increase risk of diarrhea. Under medical guidance, IV electrolyte solutions may sometimes be given during extended fasts.
Tips for fasting safely and effectively
If you’re considering fasting for health, it’s important to do so safely and effectively:
- Start with shorter fasts of 24-36 hours to see how your body responds before attempting longer fasts.
- Stay hydrated – drink water, herbal tea or bone broth.
- Listen to your body’s signals – break the fast if you experience issues like dizziness, weakness or irregular heartbeat.
- Supplement cautiously under medical supervision if fasting for longer than 5 days.
- Break a prolonged fast slowly with broths, juices and gentle foods reintroduced over several days.
- Consider working with a functional medicine doctor who specializes in fasting protocols.
The bottom line
Emerging research suggests fasting may provide healing benefits for a variety of health conditions. Likely mechanisms include lowering inflammation and switching the body into a protective state. However, large scale human studies on many specific health conditions are still lacking.
For most people, short term fasting lasting 24-72 hours is safe when precautions are taken. Further research is needed to provide more definitive answers on optimal fasting protocols for specific therapeutic purposes. As with any medical intervention, it’s important to speak to your doctor before undertaking fasting.