Quick answer: Intermittent fasting is an eating pattern that cycles between periods of eating and not eating. It focuses on when you eat rather than what you eat. People use it for weight management and metabolic health, mainly because it can reduce calorie intake and give the body longer breaks between meals. It isn’t one-size-fits-all and isn’t right for everyone.
Key takeaways
Intermittent fasting is about when you eat rather than what you eat, cycling between eating and fasting on a set schedule.
People often try it for weight management, steadier blood sugar or simply a less complicated eating routine, although food quality still matters.
The best pattern depends on your schedule and health, so a daily eating window suits some people while others prefer a couple of lighter days a week.
Fasting vs. intermittent fasting
Fasting means not eating for a period of time. Intermittent fasting is a specific pattern that cycles between eating and fasting on a schedule.
When, not what
Intermittent fasting has no rules about what to eat. That said, food quality still matters. See what to eat while intermittent fasting.
Why people try it
People try it for weight management, mainly through reduced calorie intake, and for steadier blood sugar and insulin sensitivity. Others like the simpler routines with fewer meals.
Making it work for you
Your schedule, health and preferences matter. A busy person might prefer a daily eating window, while others prefer a couple of lower-calorie days a week. Compare options in methods of intermittent fasting, and check who should not fast first.
Intermittent fasting and healthy aging
Fasting periods are thought to shift the body from growth mode to repair mode, lowering insulin, improving nutrient sensing and encouraging cellular recycling (autophagy). Much of this research is in animals, and human results vary. See autophagy.
What the research shows
Intermittent fasting has now been tested in several well-run randomized trials, which gives a clearer picture than early animal studies did.
Alternate-day fasting vs. daily calorie cutting (Trepanowski 2017, randomized trial). Researchers in Chicago assigned 100 adults with obesity to alternate-day fasting (25% of energy needs on fast days and 125% on feast days), daily calorie restriction (75% of needs every day) or no change for one year. Weight loss was the same in both diet groups at 6 months (6.8% each) and similar at 12 months (6.0% vs. 5.3%). Dropout was highest with alternate-day fasting (38%, vs. 29% with daily restriction), and LDL cholesterol was 11.5 mg/dL higher in the fasting group by month 12. A limitation is that 86 of the 100 participants were women, so the results may not apply equally to men.
16:8 eating without other changes (Lowe 2020, randomized trial). 116 adults with overweight or obesity either ate only between noon and 8 p.m. or ate three regular meals a day for 12 weeks. The 16:8 group lost an average of 0.94 kg and the regular-meal group 0.68 kg, and the difference between groups (0.26 kg) was not significant. In the in-person subgroup, the 16:8 group lost slightly more lean mass. The main limitation is the short 12-week length, and food intake was self-reported through an app.
Time-restricted eating plus calorie restriction (Liu 2022, randomized trial). 139 adults with obesity in China followed the same calorie target (1,200 to 1,800 kcal a day) for 12 months, either eating only between 8 a.m. and 4 p.m. or eating at any time. Both groups lost weight (8.0 kg vs. 6.3 kg), but the 1.8 kg difference was not statistically significant, and waist size, body fat, blood pressure and lab markers were also similar. A limitation is that the study cannot separate the effect of meal timing from the effect of calories, because both groups cut calories.
Strength of the evidence: Overall, intermittent fasting works about as well as daily calorie restriction for weight loss in most trials, but not clearly better. It is one option among several.
When to see a naturopathic doctor
It may be time to see a naturopathic doctor if you have diabetes, take blood sugar or blood pressure medication, or have a chronic condition, or if you are pregnant, breastfeeding, underweight, or have a history of disordered eating. The same is true if fasting leaves you dizzy, shaky or exhausted, or if you want a fasting approach tailored to your health goals.
See a medical provider promptly for fainting, confusion, chest pain, a racing heartbeat, or very low blood sugar symptoms such as shaking, sweating and confusion.
Want a fasting plan that fits your health?
A free 15-minute consultation with Dr. Kneessi. No cost, no obligation. In-office in Odenton, MD or by telehealth.
Questions to bring to your clinician
These questions can help you get the most out of your next visit.
Is intermittent fasting a safe fit for me, given my medications and health history?
Would intermittent fasting be safe for me, given my health history?
Which fasting schedule would be the gentlest place for me to start?
How would we know whether fasting is helping or not agreeing with me?
Frequently asked questions
What is intermittent fasting?
An eating pattern that cycles between eating and fasting periods.
Do I have to change what I eat?
No, but whole, nutrient-dense foods improve results.
Is intermittent fasting safe?
For many healthy adults, yes. Some people should avoid it or get guidance.
How does it help with weight?
Mostly by reducing total calorie intake.
Sources
- Varady KA, et al. Clinical application of intermittent fasting for weight loss: progress and future directions. Nat Rev Endocrinol 2022. PMID: 35194176. https://pubmed.ncbi.nlm.nih.gov/35194176/
- Gabel K, et al. Effects of 8-hour time restricted feeding on body weight and metabolic disease risk factors in obese adults: A pilot study. Nutr Healthy Aging 2018. PMID: 29951594. https://pmc.ncbi.nlm.nih.gov/articles/PMC6004924/
- Sutton EF, et al. Early Time-Restricted Feeding Improves Insulin Sensitivity, Blood Pressure, and Oxidative Stress Even without Weight Loss in Men with Prediabetes. Cell Metab 2018. PMID: 29754952. https://pmc.ncbi.nlm.nih.gov/articles/PMC5990470/
- Longo VD, Mattson MP. Fasting: molecular mechanisms and clinical applications. Cell Metab 2014. PMID: 24440038. https://pmc.ncbi.nlm.nih.gov/articles/PMC3946160/
- Alirezaei M, et al. Short-term fasting induces profound neuronal autophagy. Autophagy 2010. PMID: 20534972. https://pmc.ncbi.nlm.nih.gov/articles/PMC3106288/
- National Institute on Aging: Research on intermittent fasting shows health benefits
- National Institute on Aging: Calorie restriction and fasting diets: What do we know?
- Trepanowski JF, et al. Effect of Alternate-Day Fasting on Weight Loss, Weight Maintenance, and Cardioprotection Among Metabolically Healthy Obese Adults: A Randomized Clinical Trial. JAMA Intern Med 2017. PMID: 28459931. https://pubmed.ncbi.nlm.nih.gov/28459931/
- Lowe DA, et al. Effects of Time-Restricted Eating on Weight Loss and Other Metabolic Parameters in Women and Men With Overweight and Obesity: The TREAT Randomized Clinical Trial. JAMA Intern Med 2020. PMID: 32986097. https://pubmed.ncbi.nlm.nih.gov/32986097/
- Liu D, et al. Calorie Restriction with or without Time-Restricted Eating in Weight Loss. N Engl J Med 2022. PMID: 35443107. https://pubmed.ncbi.nlm.nih.gov/35443107/
This article is for educational purposes only and is not medical advice. It does not replace an individual evaluation. Talk with your healthcare provider before starting supplements or changing medications, especially if you are pregnant, nursing, or managing a health condition.
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