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Is Fasting Good for You?

By Caleb Hester · · Updated

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Have you ever felt like taking a break from food for a while and just not eating anything? Plenty of people have tried it. The real question here is, is fasting really good for you?

What is Fasting?

What exactly is fasting? How does this fit into your health plan and are there any benefits?

Fasting is when you go without food for a set period of time. That can mean skipping food for part of each day or, less often, for a full day or longer. You should keep drinking water while you fast.

Fasting is part of many religious traditions, and many people use it for weight loss. It does not "clean out" your intestines or detox your body; your liver and kidneys already do that job.

Is fasting safe?

The real question is, is fasting really good for you? Is it safe to fast?

Looking deeper into this, we need factual data to back this up and help us understand if we really should be implementing fasting in our lives.

A 2018 chart review in BMC Complementary and Alternative Medicine looked at water-only fasts done at a medical facility between 2006 and 2011.

The 768 visits included adults aged 21 and older who fasted on water only for at least two days, followed by a supervised refeeding period. Most side effects were mild, such as fatigue, insomnia, nausea, and headache, and serious problems were rare.

The key detail is that these fasts were medically supervised. That study does not show that multi-day water fasting is safe to do on your own at home.

Should You Fast

So, short fasts can be safe for many healthy adults, but does fasting have any benefits?

Here is what some of the research shows, along with its limits.

  • Weight Loss

A review of human studies found that alternate-day fasting for 3 to 12 weeks and whole-day fasting for 12 to 24 weeks reduced body weight and body fat. Fasting mostly works by helping you eat fewer calories overall.

Study: https://pubmed.ncbi.nlm.nih.gov/26374764/

  • Growth Hormone

HGH (Human Growth Hormone) plays a role in metabolism and tissue repair. In a small study of 11 young adults, a 24-hour fast raised growth hormone levels.

That does not mean fasting builds muscle. Eating enough protein and lifting weights matter far more for muscle growth.

Study: https://pubmed.ncbi.nlm.nih.gov/22386777/

  • Brain function

One study found better learning and memory in mice that followed alternate-day fasting for 11 months. Animal results don’t always carry over to people, so this is not proof that fasting boosts brain function in humans.

Study: https://pubmed.ncbi.nlm.nih.gov/23755298/

  • Heart benefits

The same review of human studies found that alternate-day and whole-day fasting lowered total cholesterol and triglycerides in some trials. High levels of both are risk factors for heart disease, though more long-term research is needed.

Heart disease background (American Heart Association statistics): https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5408160/

  • Blood sugar control

A small pilot study of 10 adults with type 2 diabetes found that daily fasting of about 17 hours led to modest weight loss and more morning blood sugar readings in the target range. Insulin resistance did not normalize, and the authors called the results exploratory.

Study: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5394735/

That study excluded people taking insulin or glyburide because of their higher risk of low blood sugar. If you have diabetes and take medication, don’t fast without your doctor’s guidance.

How to Fast

Fasting can be safe for many healthy adults and may have some benefits. So, how do you fast safely?

Here are the main options, from the most common to the most extreme.

  • Intermittent Fasting: This option is where you only eat during part of the day, such as an 8-hour window. Many people skip breakfast and eat lunch and dinner. (stay hydrated)
  • Water Fasting: This is where you go without food for a day or more while only drinking water. Fasts longer than a day should only be done with medical supervision.
  • Juice Fasting: This is where you don’t eat solid foods but drink juices. Juice is high in sugar and low in protein, and it does not "cleanse" your body.

Fasting is not a good fit for everyone. Skip it if you are pregnant or breastfeeding, under 18, have a history of eating disorders, or have diabetes or another health condition, unless your doctor approves.

Conclusion

Fasting can help some people lose weight and may improve a few health markers, but most of the benefits come from eating fewer calories. Stay hydrated, start with short fasts like intermittent fasting, and talk with your doctor before trying anything longer than a day.

Sources

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