Intermittent fasting: Starting small and building up can benefit many people

As the new year rolls over, many people vouch to eat as little as possible, and exercise as much as possible, in a desperate bid to lose weight. But, what if it was more about when you eat than what you eat?

Intermittent fasting, defined as any meal-timing intervention or approach that alternates periods of eating and extended fasting, is not a new phenomenon but has become increasingly popular in recent decades.

It is an umbrella term for various methods of fasting that restrict caloric intake, such as alternate-day fasting and time-restricted eating (TRE), though the latter represents a fundamentally different approach.

Clinical studies show the benefits of intermittent fasting for epilepsy, Alzheimer disease and multiple sclerosis in terms of symptoms and disease progression. Mechanisms by which Parkinson disease, ischemic stroke, autism spectrum disorder, and mood and anxiety disorders could benefit from intermittent fasting have been found in animal studies.

A large body of research on intermittent fasting in obese rats shows they lose weight, and that their blood pressure, cholesterol and blood glucose levels improve. However, human studies have shown intermittent fasting is safe and effective, but no more effective than any other diet.

There’s also the compliance factor to consider. As a result, TRE is now being extensively studied as a more realistic, sustainable and effective form of fasting for weight loss, as well as for diabetes prevention and other benefits (see panel).

TRE restricts caloric intake to a window of six to eight hours during a 24-hour period, unlike the typical Western eating window of 15 to 17 hours.

Predominantly based on studies with laboratory mice, TRE is hypothesised to alter metabolic regulation through its effects on circadian biology, the gastrointestinal microbiota and modifiable lifestyle behaviours. Disruptions in these circadian clock-regulated systems can increase risks of developing obesity, cardiovascular disease, diabetes and cancer due to an unfavourable metabolic network.

Based on this, researchers from the University of Alabama conducted a study in a small group of overweight men with prediabetes. One group ate all their meals in an early six-hour window, with dinner before 3pm, while the other group ate all their meals over a 12-hour period. Total food intake was matched across the two groups. After five weeks, the six-hour group had dramatically lower insulin levels and significantly improved insulin sensitivity and blood pressure, although no weight loss occurred.¹

Interestingly, several other studies have demonstrated that intermittent fasting, even in the absence of weight loss, results in a decrease in leptin and an increase in adiponectin levels, which results in improvements in insulin resistance and glycaemic control.²

Weight loss has been shown to be possible using an intermittent fasting approach in which 46 women aged 18 to 55 (BMI 25.0–34.9kg/m² ) were randomly split into two groups: one reduced their overall energy intake continuously by 25 per cent, whereas the other reduced their overall energy intake intermittently by 75 per cent on two days and ate as they liked for the other five days (ie, the 5:2 diet). Of these, 37 women completed the 12-week intervention, and 30 achieved at least 5 per cent weight loss. While both groups reduced their body weight, there were no differences in percentage weight loss or body composition between the two groups.³

Fasting from sunrise to sunset during the holy month of Ramadan is a well-known feature of Islam. According to a 2012 meta-analysis of 35 studies, weight changes were seen in those who fasted during Ramadan. The subjects, aged between 18 and 58, showed a 1.24kg weight reduction during this practice.⁴

Further studies have reported attenuated levels of fasting blood glucose, low-density lipoprotein cholesterol, C-reactive protein, interleukin-6 and tumour necrosis factor alpha associated with Ramadan fasting.

An overnight fast of at least 10 to 12 hours can be further leveraged by extending it out either side

Glycaemic control is also improved during Ramadan fasting, and recent studies provide evidence to suggest there is a 0.5-point decrease in HbA1c levels in patients with type 2 diabetes after fasting during Ramadan.⁵

A case series by Furmli and colleagues in 2018 followed three patients with type 2 diabetes over several months after beginning an intermittent fasting regimen consisting of three 24-hour fasts per week. Throughout the study, all three patients had significant reductions in HbA1c, lost weight, and were able to stop their insulin therapy within one month. Of note, no patient stopped the intervention at any point out of choice.⁶

Camilla Dahl, a dietitian and nutritionist at Diversa Health in Melbourne, is a particular advocate for fasting in patients with type 2 diabetes. She states that the longer you fast, the lower your insulin gradually becomes, which allows the body and insulin to reset and resensitise. For this reason, an overnight fast of at least 10 to 12 hours can be further leveraged by extending it out either side. This seems more realistic for the general population too.

Many are concerned about a loss of muscle mass during periods of fasting, but it is known that growth hormone protects against this loss in the short term. Hypoglycaemia is possible with fasting in those with type 2 diabetes, and symptoms such as extreme fatigue and nausea would warrant an immediate cease of any fasting regimen. However, Ms Dahl states that 90 per cent of symptoms from a fast can be linked to a sodium deficiency.

She also says that a lower-carbohydrate diet can be trialled before fasting, which is supported by the US Academy of Nutrition and Dietetics for those with type 2 diabetes. This is not supported by Ministry of Health guidelines, however. Long-term studies of those following restricted-carbohydrate diets show they are no more effective for weight loss after 12 months than a healthy eating approach. Healthy eating according to ministry guidelines is also effective at reducing many of the risk factors associated with diabetes and cardiovascular disease.

While fasting isn’t for everyone, optimising your migrating motor complex is. A dysfunctional MMC is believed to be one potential contributor to the development of small intestinal bacterial overgrowth (though not the root cause). Four to five hours between meals is seen to be ideal for the MMC “cleaning waves” to avoid small bowel bacterial fermentation and growth.

Fiona Kendall is a registered dietitian at Dietary Specialists private practice in Christchurch