What are the benefits of intermittent fasting and is it for everyone? Dr Catherine Crofts takes a look at the evidence around different types of fasting for improved health.

Who Should Consider Intermittent Fasting? Almost everyone.

Fasting for some people might feel a lot like climbing a mountain. But the reality is that almost everybody should consider fasting as part of a healthy lifestyle. Fasting doesn’t necessarily have to be onerous. There’s a lot of evidence to support intermittent fasting to improve health. We know that fasting can help to improve weight loss, especially with reduction of visceral fat, improving insulin resistance, lowering hyperinsulinemia, improving inflammation, and other markers of inflammation, such as triglyceride levels. It also improves markers of brain health, including BDNF (brain-derived neurotrophic factor), and it may help to prevent certain cancers or improve the prognosis of cancer.

“Evidence supports intermittent fasting for conditions such as type 2 diabetes, cancer, cardiovascular disease, dementia, multiple sclerosis, and other autoimmune conditions.”

There are lots of different types of intermittent fasting. Some are very short, less than 24 hours. Others are multi-day. And there’s some evidence to suggest that longer fasts may confer additional or greater benefits for some people in certain conditions, but only up to a point.

Fasts of 14 to 10, where you fast for 14 hours and you have a 10-hour compressed eating window, are considerably safe for most people.

“There’s always going to be exceptions to the rule, but fasting for 14 hours overnight is probably safe and healthy for most people.”

Ideally, the last meal should be at least three hours before bedtime, as this may help to reset the circadian rhythm. This may benefit people who are shift workers or those who suffer from insomnia.

Compressed eating windows in intermittent fasting – a good compromise

Compressed eating windows could be anything from fasting for 16 hours and eating for eight hours during the day; smaller opportunities such as 20 to four; or even the warrior lifestyle, where people only eat once a day. There is evidence to show that the compressed eating windows can augment the lifestyle management of metabolic diseases, especially type 2 diabetes and cardiovascular disease, as it helps to keep the insulin levels lower for a lot longer, helps to mobilise the fat stores, mobilise the body’s defence mechanisms and immune systems.

Some people recommend compressed eating windows as a building block towards a multi-day fast. Often compressed eating windows are more recommended when multi-day fasts are not appropriate. Because remember, not all fasting systems are appropriate for everybody at every health stage. But compressed eating windows can sometimes be a very good compromise.

Limited evidence for water fasts

Another type of fast is water-only fasts of two to three days, or even longer durations for some people. Now, this is where we’ve got a lot more limited evidence. There is some evidence to suggest that a water fast two days before chemotherapy and for one day afterwards, or with some other forms of cancer therapy, can augment the cancer therapy and minimise the side effects. I want to emphasise that there is only limited data around this.

Water fasts have also been used for seizure management and for helping people to get into ketosis faster. There’s some evidence to suggest that a water fast can help to reset the immune system. Now, I’m going to stress with the water fast, especially for slightly longer durations, and especially if there are other medical conditions involved, that medical supervision is often necessary. Electrolyte management is critical. Fasting with bone broth, and for some people coffee, may be more suitable than a water only fast.

Fasting caveats

There are a lot of caveats with the evidence that we have around fasting. Most human studies only have small numbers. We’ve got a limited amount of data. Other studies on rats show how the benefits of fasting can be seen. And we know from other work that rodent studies don’t always equate through to human physiology. So, we have to take that information with a little bit of caution.

We also need to be aware of safety, especially when you’re moving towards very compressed eating windows, such as once daily or multi-day water fasts. We need to make sure that it’s safe and done with appropriate medical oversight.

But after considering those things, fasting can be a great addition to many lifestyle approaches to health.

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