Last Saturday the Times here in the UK published a piece I wrote about ‘intermittent fasting’. This topic has been getting a lot of press of late (the Daily Mail, for instance, carried a piece earlier this week too). I’m pleased to see that intermittent fasting is getting some attention, and there’s some challenge to the ‘3 meals a day’ mantra that I, until recently, subscribed to myself. Intermittent fasting is not for everyone (see below), but I’ve seen it help people control their weight and improve their wellbeing. I’ve also met lots of individuals who eat quite erratically and have believed that they are harming themselves doing this, look at their eating habits in a new and healthier light.
Why Fasting is the New Way to Lose Weight (and Live Longer)
“Eat three meals a day” has been part of dietary and weight loss dogma for decades. However, recently, there has been growing interest in what is known as ‘intermittent fasting’, the practice of food restriction that may involve extended periods, sometimes whole days, without eating. While intermittent fasting appears to contradict an essential credo of healthy eating advice, there is evidence that it can enhance body composition and health and may even extend life.
While eating is undoubtedly essential to life, it has inherent hazards too. For example, when we eat, we secrete the hormone insulin which facilitates the uptake of nutrients, including fat, into cells. In general terms, the more insulin we secrete, the fatter we get, and the more likely we are to become ‘numb’ to the effects of insulin over time too. This situation, termed ‘insulin resistance’, can lead to a ‘starving’ of the cells, provoking symptoms such as fatigue and hunger. Insulin resistance is also a potential driver of chronic diseases such as heart disease, Alzheimer’s disease and type 2 diabetes.
Quelling insulin will help protect against these conditions, and will facilitate fat loss too. One way to quell insulin levels is to eat a diet largely devoid of the foods that cause surges in blood sugar such as those added sugar as well as starchy ‘staples’ like bread, potatoes, rice pasta and breakfast cereals. Another way, though, to moderate insulin levels is to extend the time between eating. This, in essence, is what intermittent fasting is about.
Intermittent fasting experiments in animals has found improvements in markers for disease, including improved insulin functioning, as well as enhanced brain health. There is some encouraging human research too. In one study published last year, overweight and obese women undertook daily or intermittent caloric restriction over a 6-month period . Half the women restricted food intake to 1,500 calories a day. Those on the intermittent fasting regime, on the other hand, ate 650 calories on each of two days each week, and were free to eat as much as they liked the rest of the time.
Both groups lost similar amounts of weight (an average of about 6 kg), and also saw improvements in measures such as blood pressure and inflammation. Insulin levels fell and insulin functioning rose in both groups too, but it did so more in the intermittent fasters. Another potential benefit of intermittent fasting is that, compared to daily caloric restriction, it appears to help preserve muscle mass during weight loss .
How to do it
One type of intermittent fasting is known as ‘alternate day fasting’. In essence this means having food-free days alternating with days of unrestricted eating. Other forms of intermittent fasting include contracting the ‘window’ available for eating each day to, say, 4-8 hours. For many, these approaches are impractical and simply too arduous. The good news is that less extreme and more realistic versions of intermittent fasting can reap significant dividends.
One approach could be to extend the period of low insulin typically seen at night. An early dinner or delayed breakfast will do this. As the body becomes more accustomed to lower insulin levels, its ability to mobilise fat will be enhanced. This fat provides fuel for the body, and is a potential source of sustenance during extended periods without food. Once the body is more adept at burning fat as its primary fuel, it’s less reliant of food for fuel and energy. When the body ‘feeds off its fat’, one’s ability to go without food and not suffer undue hunger, fatigue or issues with brain function is enhanced. I’ve seen many individuals who, after several weeks of low-carb eating and some experimentation with intermittent fasting are amazed at the length of time the can go without getting unduly hungry or experiencing and loss of energy or drop in mental functioning.
Once the body is better adapting in this way, the next step might be to drop some breakfasts or dinners altogether. My advice would be to drop the one you feel is going to be easiest to do without. If you’re generally hungry in the morning and find your appetite tails off at the end of the day, then dinner is perhaps the best to forgo. If you usually have little appetite in the morning, then missing breakfast is likely to be a better for you.
There’s no reason to be rigid with intermittent fasting either. If you tend to skip breakfast with ease but, say, find yourself uncharacteristically hungry one morning, then you may benefit from eating something that day.
On days where you’re intake of food is significantly reduced, it pays to emphasise foods that are highly nutritious and effective at sating the appetite. Protein and fat tend to pack most punch here, so appropriate foods might be fresh meat, oily fish, eggs and nuts, coupled with some green vegetables and salad for additional nutrients.
It’s important to remember that intermittent fasting does not need to be an endurance exercise. The aim is not to see how hungry one can get before caving in. This tactic usually backfires, because it will often drive people to eat frankly unhealthy foods. I advise gradual change, effectively training the body over time in a way that is practical, flexible and does not induce undue hunger.
Not for Everyone
Intermittent fasting has merit, I think, but it’s not for everyone. Those who should avoid intermittent fasting include individuals with a history of eating disorder and diabetics. Other individuals who are generally unsuitable candidates for intermittent fasting include those who are generally ‘stressed’ or have chronic fatigue. Stress can weaken organs known as the adrenal glands, and intermittent fasting can weaken these glands further, which may exacerbate symptoms such as fatigue. Individuals who are seeking to optimise their sporting performance should approach intermittent fasting with care, particularly if they are in an active phase of building muscle and strength. Working with a fitness professional with experience of intermittent fasting is advised. Those in any doubt about the appropriateness of intermittent fast for them should seek the advice of a doctor before making any changes.
1. Harvie MN, et al. The effects of intermittent or continuous energy restriction on weight loss and metabolic disease risk markers: a randomized trial in young overweight women. Int J Obes (Lond) 2011;35(5):714-27
2. Varady KA. Intermittent versus daily calorie restriction: which diet regimen is more effective for weight loss? Obesity Reviews2011 Jul;12(7):e593-60