Written by Kaci Oliver, MS, RD, LDN
Lately, a lot of my patients have asked me about intermittent fasting as a way of weight loss. I am here to break down the pros and cons of intermittent fasting, and to take a look at what the science actually says.
What is intermittent fasting?
Fasting, meaning to abstain from food or drink for periods of time has been practiced for centuries by people all around the world, usually for religious purposes. Recently, intermittent fasting has become popular for weight and health purposes. Intermittent fasting can help drive weight loss by decreasing daily calorie intake, and by inducing a ketogenic state which requires the body to use more energy, leading to greater calories burned.
There are three main forms of intermittent fasting being utilized for weight and health; the complete alternating day fasting method, the modified fasting regimen, and the time-restricted feeding method.
| Alternating Day Fasting | Alternate fasting days (no energy-containing foods or beverages consumed) with eating days (foods and beverages consumed ad libitum) |
| Modified Fasting or 5:2 diet | Involves limiting energy consumption to 20% to 25% (500-600 calories) of energy needs on 2 nonconsecutive days a week and eating ad libitum the other 5 days. |
| Time-Restricted Feeding | Limits individuals to consume food and beverage ad libitum within specific windows (usually 6-8hrs), which induces fasting periods on a routine basis. For example, a person may only eat from 12-8pm or 12-6pm during the day depending on how intense their fasting is. |
No one fasting method is considered better than the others; however, it is important to work with a dietitian to find the one that is best for you in fitting in with your lifestyle and meeting your goals.
Benefits of Intermittent Fasting:
Weight loss: Multiple studies have found significant weight loss for all three fasting methods. One study found that participants who participated in alternate day fasting for 22 days showed a 2.5% weight loss. A 3.5%-8% weight loss was found in participants who completed 5:2 diet fasting for 8-12 weeks. Another study found men who underwent time-restricted intermittent fasting had a significant 1.3% weight loss over the course of 2 weeks. Another crossover study compared the effect of consuming one afternoon meal per day for 8 weeks and reported 4.1% weight loss in comparison to a stable, low-calorie diet consumed as three meals per day.
Increased insulin sensitivity: A study conducted in mice found that alternate day fasting had a significant impact on improving insulin sensitivity and reduce glucose concentrations. Another study found that participants who completed the 5:2 fasting method for 6mo had a decrease in fasting insulin concentrations.
Reduced cholesterol, especially triglycerides: Studies have found significantly reduced lipids levels after completing 5:2 diet fasting for 8-12 weeks. A study found that participants who completed time-restricted feeding by only consuming 1 meal/day had lower LDL and HDL cholesterol levels after 8 weeks.
Reduced inflammatory markers: Two studies have found significant improvements in inflammatory markers, including C-reactive protein, tumor necrosis factor-alpha (TNF-a), adiponectin, and leptin after practicing the 5:2 diet for 8-12 weeks.
No calorie counting: intermittent fasting could be a less time consuming and easier method of weight loss than worrying about counting calories, making it easier to stick to.
Negative Side Effects of Intermittent Fasting:
In healthy, adults, there is little evidence that intermittent fasting regimens are harmful physically or mentally. However, some negative side effects of intermittent fasting found in studies include: feeling cold, irritable, dizzy, low energy, constipation, headaches, blood sugar fluctuations or hunger.
Populations who should avoid intermittent fasting include: pregnant or breastfeeding women, children under the age of 18yo, those who suffer from hypoglycemia, people recovering from eating disorders, underweight or malnourished individuals, those taking certain medications (i.e. fast-acting insulin), and women with abnormal menses.
Is Intermittent Fasting Right for You?
While there are a few, short-term studies that show intermittent fasting can assist with weight loss, reduce chronic disease risks such as diabetes and hyperlipidemia, and reduce inflammatory markers, there is more long-term research needed. Just like any other lifestyle approach to weight loss, it is important to speak with your physician and/or dietitian to determine if intermittent fasting is right for you. Call our office today at 336-610-1300 to make an appointment.
References:
- Patterson et al (2015). Intermittent Fasting and Human Metabolic Health. Journal of the Academy of Nutrition and Dietetics. 115 (8). Intermittent Fasting.pdf
