Losses and gains of intermittent fasting

Bidding farewell to chametz, fasting for 12 or 24 hours, and eating up a storm when it’s all over. While, as Jews, we’re used to overhauling our diets and observing fast days, practising intermittent fasting takes a different kind of commitment.

“Intermittent fasting is based on the concept not of what you’re eating, but when you’re eating,” says dietitian Elise Barron. It looks at weight loss in a different way and ultimately helps to promote fat loss, control appetite and preserve muscle mass.

Arguably, the best-known version of intermittent fasting is time-restricted eating (TRE). “Time-restricted eating limits the eating window to a specified number of hours each day, typically four to eight hours,” says Dr Charlene Wolberg, a medical doctor and nutritionist. “The remaining hours of the day are fasting, with water or zero-calorie drinks.”

“It’s important to start slowly and ease one’s way into the diet,” Wolberg cautions. “There may be an adjustment period of one to three weeks. Headaches are often experienced initially, but subside when water intake is increased.”

“Intermittent fasting is a lifestyle, it’s not a diet,” argues general practitioner Dr Lana Marcus, who has been practising TRE for five years. She has an eight-hour eating window, followed by 16 hours of fasting. “It can be used as a tool for weight loss, as anything that restricts the number of calories you eat will lead to weight reduction,” she says.

However, many who follow intermittent fasting choose to do so as a health measure as opposed to a weight-loss strategy, Marcus says. Intermittent fasting was recommended to her when she was diagnosed with polycystic ovary syndrome, a hormone imbalance linked to insulin resistance and metabolic syndrome.

Marcus felt the effects relatively quickly and observed dramatic results in her bloodwork. “I managed to reduce my triglyceride [a type of fat in the blood called lipid] levels by 20% and I felt more energised,” she says.

Marcus explains how intermittent fasting can boost one’s metabolism. “When we eat, particularly if we’re having a carb-dense meal or refined carbs, we release a lot of glucose into our bloodstream,” she says. “Rather than having that glucose float around in the bloodstream, the body wants to pack it away into the tissues for energy utilisation and storage. This is where insulin comes in.”

Insulin encourages lipogenesis, so it converts more carbohydrates into fat, explains Barron. “Insulin also inhibits lipolysis, where the body blocks the use of stored fats. So with intermittent fasting, there’s typically a decrease in insulin and, as a result, the body can then use glucose and fat for fuel. Less insulin also helps to balance hunger.”

Other benefits include increased production of brain-derived neurotrophic factors important for brain health and cognition, says Barron. People therefore often report an increase in focus. While it can sometimes therefore decrease anxiety and depression, conversely intermittent fasting can increase cortisol levels, boosting feelings of stress. “To mitigate cortisol impact, exercising, good quality sleep, and stress management are important,” Barron says.

“As a mild stressor, fasting is beneficial in moderation, but harmful if the body is already under significant physical or emotional stress, including hormonal issues,” adds Leigh-Ann Silber, a registered dietitian and nutrition consultant.

“It’s particularly important not to binge at the end of the fasting period,” Marcus says, discussing the correct approach to food intake. “Rather, break your fast with high fibre, high-protein foods because having too many carbs straight off the fasting period will spike blood sugar and possibly make you feel unwell. Meal planning is therefore important, regardless of whether you’re trying to lose weight or not.”

In Barron’s experience, intermittent fasting doesn’t work for everyone. Possible downfalls include the fact that it’s difficult to maintain in social situations, especially when eating out at certain times. “For some people, it also creates hunger and irritability,” she says.

“People also sometimes make poor food choices, because they know they’re eating only two meals a day or within a smaller space of time. Some land up overeating in the afternoon or after dinner because their sugar levels are dropping. Typically, it’s a form of eating that isn’t sustainable in the long term,” she says.

Silber says for most healthy individuals, intermittent fasting – especially TRE eating like 16:8 or even 12:12 – can be a safe and effective approach to support weight management, improve insulin sensitivity, and promote cellular repair.

But it isn’t safe or beneficial for everyone “It should be personalised and guided by a professional to avoid any negative effects and to ensure it’s beneficial. Like any eating pattern, it isn’t one-size-fits-all. There are some potential downsides particularly with more extreme fasting windows like 20:4 or one meal a day.”

Eating a large amount in a short window like four hours, Silber adds, can overwhelm the digestive system, leading to bloating, nausea, or indigestion. “This may make it harder to meet daily nutritional needs, especially if meals aren’t well-balanced. Prolonged or aggressive fasting can also affect the menstrual cycle or thyroid function in some women, particularly if calorie intake is chronically low.”

Intermittent fasting is not recommended for children, pregnant or breastfeeding women, those with a history of eating disorders, or for individuals with low blood pressure, diabetes or low blood sugar issues.

“Those with high-energy needs like teenagers, athletes, and individuals with physically demanding jobs may struggle to meet their nutritional needs in a restricted time window,” Silber says.

Those who attempt intermittent fasting will know within three to five days if it works, Barron says. “If your appetite is controlled, your focus is good, your energy levels are optimal throughout the day and two meals a day are enough, it’s probably beneficial. If it doesn’t work for you, you’d be tired, grumpy, irritable, overeating, and thinking of food all day.”