Intermittent Fasting: What Do We Know?

A Scale and Tape Measure

Intermittent fasting is a technique whereby a person withholds food on a regular basis intermixed with periods of normal eating. There are numerous different ways the technique is applied, including fasting one or two days a week, to only eating within an eight-hour window. While the research on intermittent fasting is in its infancy, there are strong suggestions of benefits. 

Throughout most of our ancestors’ lifetimes, food scarcity was more the norm than the exception. The body has evolved mechanisms to survive when times are lean. With food now being more plentiful, intermittent fasting may help mimic lean periods, providing weight loss and other health benefits.

From what we know so far, it appears that intermittent fasting may help with:

  • Losing weight
  • Controlling blood sugar
  • Improving heart health
  • Preventing cancer
  • Protecting brain health

Intermittent Fasting and Weight Loss

Probably one of the most common reasons people explore intermittent fasting is a means to achieve successful weight loss. By reducing the number of calories you consume on a regular basis, you will typically start to lose weight. And with intermittent fasting you can have “normal days” interspersed among diet days, which may help some people to feel less deprived. Long term, the weight loss benefits will likely remain if the intermittent fasting regimen is maintained. However, if the intermittent fasting program is halted, the individual may regain the lost weight. 

One trial compared a low-calorie weight loss diet to consuming 25% of calories every other day with 125% of calories on the “feasting days” in between. Both approaches led to weight loss, although the intermittent fasting diet was harder for patients to maintain (Trepanowski 2017). A separate comparison of a low-calorie diet to eating only 25% of calories two days a week found the diets to be comparable in efficacy (Harvie 2011). A Similar trial using two restricted days per week also found similar benefits to a standard low-calorie diet for weight loss. However, the individuals on the intermittent regimen noted more hunger on the restricted days (Sundfor 2018).   

While intermittent fasting does appear to be effective for weight loss, it may require more self-control than a standard calorie-restricted diet. Improvements in other health parameters appear to be similar to standard weight loss regimens. 

Intermittent Fasting and Blood Sugar Control

Blood sugar problems are common, especially as we get older. If left unchecked, blood sugar problems can easily lead to diabetes. In patients with high blood sugar or diabetes, intermittent fasting may help with blood sugar control, although there are risks for low-blood-sugar episodes (Corley 2018). If an individual’s blood sugar drops too low, it can be life-threatening. In diabetic patients, a one-week fasting period that consisted of only 300 liquid calories per day was found to provide weight loss benefits, improved blood pressure and increased quality of life (Li 2017). 

In individuals with prediabetes, consuming all calories within a six-hour window before 3 PM was found to improve insulin sensitivity, blood pressure, antioxidant levels and appetite (Sutton 2018). For diabetics, a standard low-calorie diet was compared with an intermittent fasting regimen and was found to be functionally equivalent (Carter 2016). As long as it is done carefully, under proper supervision to treat low-blood sugar episodes, intermittent fasting appears to be an option for helping to improve blood sugar and other parameters in diabetes. 

Intermittent Fasting and Heart Health

Restricting calories in general can help with losing weight, decreasing blood pressure and improving blood sugar levels. All of these factors can help improve heart health. In overweight individuals, alternate day fasting was found to lower LDL cholesterol, reduce waist circumference and decrease body fat, improving heart disease parameters (Bhutani 2010). 

One trial even compared high-fat, alternate-day fasting to standard dieting and found the heart disease benefits to be equivalent. Total weight, body fat and LDL (bad) cholesterol were all reduced (Klempel 2013). Considering the greater pleasure and satisfaction from consuming high-fat foods, it’s interesting to have healthy ways to include them. 

A separate diet that focused on eating within an eight-hour window found reductions in weight, body fat and waist circumference. This intermittent fasting routine reduced heart disease risk by a modest 12% in obese women (Schroder 2021).   

Intermittent Fasting and Cancer

Some Intermittent Fasting Routines Just Have Windows of Reduced Calories

Animal studies have found that fasting in animals with cancer decreases the toxic effects of chemotherapy and improves outcomes. A trial in patients with breast cancer found similar effects with decreased cell damage from chemotherapy and improved therapeutic responses (Groot 2020). An earlier pilot trial for breast and ovarian cancer found that a short-term fast during chemotherapy improved quality of life and decreased fatigue (Bauersfeld 2018). Individuals that followed a four-week fasting program that disallowed calories from sunrise to sunset were shown to have an anti-cancer-induced shift in gene expression (Mindikoglu 2020).

While more research is necessary, the preliminary results suggest that intermittent fasting may yield benefits for cancer prevention and treatment. 

Intermittent Fasting and Brain Health

Alzheimer’s disease, the most common type of dementia, has become a global epidemic. And with no standard treatments available that improve long-term outcomes, prospects for treatment are currently somewhat dim. 

Of interest, animal studies appear to indicate that intermittent fasting may have a role for treating dementia. In a mouse model of dementia, intermittent fasting preserved brain cells and improved cognition (Andika 2021). In a separate mouse model of Alzheimer’s dementia, both intermittent fasting and calorie restriction were found to improve behavior and cognitive function (Halagappa 2007).  


Intermittent fasting is a reasonable alternative to a low-calorie diet. It appears to provide similar benefits for weight loss, blood sugar control and heart disease. While often touted as an easy weight loss alternative, the research indicates that intermittent fasting is likely harder to maintain than a low-calorie diet. And while beneficial in patients with diabetes, there is an increased risk for low-blood-sugar episodes which could be severe. However, for those with the willpower to follow an intermittent fasting routine, the benefits may be significant and worth pursuing. 

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