Diet trends come and go, but the newest dietary craze—intermittent fasting—can actually trace its roots to the days of the caveman.
Our ancestors practiced intermittent fasting (IF) due to food scarcity, but this ancient survival adaptation might also serve as a tool for improving health. Recent short-term studies have shown intermittent fasting’s potential for improving many critical health markers.
“Intermittent fasting can be an effective tool for weight loss, blood sugar and blood pressure control, and improving heart health,” says Christine Maren, DO, a family medicine physician in Colorado who incorporates a holistic nutritional component into her functional medicine practice. “It is also a catalyst for autophagy, your body’s process of cell regeneration.”
What is intermittent fasting?
Intermittent fasting, for the uninitiated, differs from other diets in that it doesn’t necessarily restrict what a person eats but rather when they eat it. People who are practicing intermittent fasting cycle between brief periods of fasting, with either no food or significant calorie reduction, and periods of unrestricted eating.
The three main methods of intermittent fasting are:
- Time-restricted feeding: Eating within a designated window of time. For example, meals are eaten between 10 a.m. and 6 p.m. only; you fast the remainder of the day.
- Alternate-day fasting: Alternating between days of no food restriction with days that consist of one calorie-restricted meal providing about 25 percent of a person’s daily calorie needs. For example, Mon-Wed-Fri fasting, with no food restrictions on alternate days.
- 5:2 whole-day fasting: This plan entails two days per week of complete fasting with no food restriction on the other five days. Some patients may include a 400-500 calorie diet on the two fasting days.
From improved mental clarity and energy levels to weight loss and reduced insulin resistance for Type 2 diabetics, intermittent fasting has been shown to improve critical health markers in some short-term studies and case reports. It should be noted, however, that there is no long-term data on intermittent fasting yet, says Tiffany Lowe-Payne, DO, a weight loss and stress reduction expert, and much of the research is on animals.
Some of the newer research includes a 2017 study by scientists from Harvard T.H. Chan School of Public Health. They found that adopting dietary restrictions such as fasting from time to time could manipulate mitochondrial networks inside cells and might increase lifespan.
A University of Alabama study on a small group of obese men with prediabetes concluded that restricting your calories even further than the prescribed IF methods (by eating all of them before 3 p.m.) can improve metabolic health even in the absence of weight loss. Study participants who restricted their eating this way had dramatically lower insulin levels, significantly improved insulin sensitivity and blood pressure and a decreased appetite.
A DO’s experience
Dr. Maren’s functional medicine practice sees many patients with digestive issues such as small intestinal bacterial overgrowth (SIBO) and irritable bowel syndrome (IBS). “Intermittent fasting can be a good way for these patients to rest and give their digestive process a chance to recover,” Dr. Maren says. “Typically patients with SIBO feel a lot better practicing IF because they’re not feeding the bacteria.”
When to approach with caution
Patients with the following conditions should seek the care of a physician before embarking on an IF regimen, according to Dr. Lowe-Payne:
- Blood pressure issues, such as low blood pressure (because it will further lower it)
- Women trying to conceive
- Pregnant women
- Women or men with a history of eating disorders
- Women who may not get a menstrual cycle or who have hormone regulation issues
- Patients at risk for hypoglycemia, such as insulin-dependent diabetics
- People on multiple medications
- People with physically demanding jobs or who exercise rigorously (and thus have higher fuel demands)
Guidance for patients
If your patient is interested in trying intermittent fasting, here is some advice to share.
Stay well-hydrated. Many people think that fasting means not eating or drinking anything, but you need to make sure to drink plenty of fluid. That can include water or unsweetened teas, Dr. Lowe-Payne says.
Monitor caloric intake. Patients should make sure they’re getting the number of calories they need for their basal metabolic rate, Dr. Lowe-Payne says. If not, this can lead to a sluggish metabolism and hitting a plateau.
Women should monitor their response to the diet closely. Dr. Maren finds that female patients tend to do well with IF, but they often don’t tolerate prolonged fasts, which indicates a possible hormonal component. “For women struggling with hormonal imbalances, it’s really important to listen to your body while practicing intermittent fasting,” Dr. Maren says.
Cycle in and out of IF. For most people, it helps to cycle in and out of intermittent fasting. “You do not want to stay on it long-term,” says Dr. Lowe-Payne. “Stick to 3-4 days a week. Doing it as a lifestyle every day can slow your metabolism.”
Know when to back off. If a patient experiences weakness, trouble sleeping, cardiovascular side effects, dizziness or any signs of electrolyte disturbance, they should back off of intermittent fasting, Dr. Maren says.