THREE meals a day starting with a hearty breakfast – the so-called most important meal – and regular snacks to keep the body fuelled.
This is the conventional wisdom about what constitutes healthy eating.
But there is a growing body of research supporting the view that our bodies and brains have evolved to function optimally when they receive food only intermittently, and that periods without eating have the same healing effect as sleep. Other claims for intermittent fasting are that it can enhance our ability to cope with stress by making cells more resilient, improve mental and physical performance and protect against ageing and disease.
It's not about calorie restriction or what you eat. It's all about when you eat, and means frequent periods with little or no food – something that rarely happens in the modern developed world, where for many people food is available 24/7.
Weight loss is one side effect, but according to Dr Mark Mattson – a professor of neuroscience at Johns Hopkins University who has studied intermittent fasting for 25 years – the added benefits include slowing the effects of ageing, reducing the risk of diseases (including cancer, obesity, diabetes and Alzheimer's) and enhancing body and brain function.
In his book The Intermittent Fasting Revolution: The Science of Optimizing Health and Enhancing Performance, Mattson tells of how he became aware of the “anti-ageing” effect of caloric restriction in the early 1990s. Because ageing is the major risk factor for Alzheimer’s and Parkinson’s diseases and stroke, he recruited several post-doc scientists to immerse themselves in research around intermittent fasting, wanting to understand the potential neurological benefits.
The first studies were on rats or mice and found that when maintained on an every-other-day fasting regimen, neurons in the rodents' brains became more resistant to dysfunction and degeneration in experimental models of Alzheimer’s, Parkinson’s and stroke. There were also “very profound improvements in blood sugar regulation, cardiovascular stress resistance, and physical endurance".
The effects were just as impressive in humans. According to Mattson, intermittent fasting reduces “body composition" (fat) and “glucose regulation" but also inflammation and “oxidative stress".
Evolution
In her book Fast Like a Girl, Dr Mindy Pelz says the concept goes back to the so-called “thrifty gene” hypothesis. Some scientists believe the harsh conditions under which our prehistoric ancestors lived, with periods of feast and famine, created a genotype that still exists.
“Ramadan fasting is one of the greatest examples of how the human body positively adapts to long windows of time without food. In fact, some of the best fasting research has been birthed out of studying the Muslim community during Ramadan."
A 2019 paper in the authoritative New England Journal of Medicine outlined the findings of one the most comprehensive analyses of the science of fasting. Mattson and a co-author reviewed more than 85 studies on intermittent fasting and stated that “when considered in the light of evolution, it becomes obvious that intermittent fasting eating patterns are normal, whereas three meals plus snacks are abnormal. During evolution, individuals whose brains and bodies functioned very well when they were in a food-deprived state were those who survived and passed their genes on to the
next generation."
The paper suggested that intermittent fasting should be the first line of treatment for obesity, diabetes, cardiovascular disease, neurodegenerative brain conditions and cancer. Another conclusion, based on “nearly a century of research on caloric restriction in animals", was that reduced food intake “robustly increases the life span".
Metabolic switch
To understand how to apply intermittent fasting, it is useful to understand that there are two main nutritional sources of energy for our cells: sugar and fatty acids.
Pelz explains it simply: “The first system, called the sugar-burner energy system, gets activated when you eat. Eating food raises your blood sugar. Your cells sense this influx of sugar in your blood and use that sugar, called glucose, as fuel for the thousands of functions they perform. When you stop eating, your blood sugar drops. This slow decline of glucose in your blood triggers your cells to switch over to the second energy system, called the ketogenic energy system, or what we lovingly call the fat-burner system. Very much like a hybrid car that switches from gas to electric for fuel, this switchover is when the fasting benefits begin."
The “metabolic switch" is when the body starts using energy stored in fat cells, but that point is not the same for everyone. The biology of men and women differs vastly and genetic factors also have an influence. Research shows, however, that it takes 8-12 hours of fasting to deplete liver glucose stores and switch the body to using ketones produced from fats.
Different fasting patterns
Mattson says the three most popular intermittent fasting eating patterns are daily fasts of 16-20 hours, often referred to as “daily time-restricted eating”; fasting two days a week, or “5:2 intermittent fasting”; and fasting five days in a row every month.
He says the easiest way is to start gradually, taking several months to reduce the daily time window during which you consume food with the goal of fasting for 16-18 hours. On a 16-hour daily fast, you will condense the period in which you consume meals to eight hours. And on an 18-hour daily fast, you will have a six-hour window in which to eat.
Initially, says Mattson, many intermittent fasters will experience hunger, irritability and a reduced ability to concentrate during periods of food restriction. However, these side effects usually disappear within a month, and patients should be advised of this fact.
Ultimately, however, says Pelz, “many fasters feel so productive in the fasted state that they want to stay there throughout their day … [but] eventually you’ll need to switch back to your sugar-burner system to fuel your brain. It’s moving in and out of both energy systems that provides the brain with all the necessary fuel it needs to perform at its best."
There have been no direct comparisons of the health benefits of different intermittent fasting approaches but each has been shown to improve health indicators when compared to a breakfast, lunch, dinner and snack eating pattern.
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Women and men
Women and men need to approach intermittent fasting differently, says Pelz. “Men are hormonally simpler. They have a 24-hour hormone cycle with one main hormone – testosterone – moving in and out of their bodies every 15 minutes. Men don’t have the ebbs and flows of estrogen and progesterone to contend with."
Interestingly, studies show that fasting can dramatically increase testosterone levels in men. Pelz says: “Testosterone loves fasting. There can be up to a 1,300% increase in testosterone if men fast for 13 hours, and up to 2,000% if they fast for 24 hours."
Pelz says women should adapt the way they fast to where they are in their menstrual cycle because of the “symphony of hormones". You should not fast “against the natural groove of your hormones", she cautions.
At the beginning of your cycle (the first 10 days after day one of your period), estrogen starts building up in your body. This is a good time for longer periods of fasting because estrogen thrives when insulin is low and this is what fasting achieves: low insulin levels. During the next phase, the ovulation window, there are three hormones at play: estrogen and testosterone surge and there is a tiny bit of progesterone. During this time you should adapt your fasting to a more moderate level, and in the week before your next period you should avoid fasting altogether because this is when progesterone builds up.
“Progesterone prefers you to keep glucose on the higher side. Any diet that keeps glucose low, like the ketogenic diet, will also negatively impact your progesterone levels. These two influences on progesterone make fasts of all lengths a terrible option the week before your cycle."
What to eat
Intermittent fasting is not a diet but the principles of good nutrition remain important and relevant. “It turns out that there is nothing particularly unique to the brain when it comes to diet composition. What is bad for the heart is bad for the brain, and what is good for the heart is good for the brain," says Mattson.
“Bookstore shelves have recently become riddled with ‘keto’ and ‘paleo’ diet books. But the truth is that the scientific evidence shows that there are three simple principles for healthy eating. First, avoid the consumption of simple sugars (glucose, fructose, sucrose), heavily salted foods, fried foods and highly processed foods. Second, consume a variety of vegetables, fruits, nuts, whole grains, beans and fish, as well as moderate amounts of milk products. Third, cook with extra virgin olive oil."
Final word
Mattson says he and his family have adopted an eating pattern in which most days they skip breakfast then eat during an eight-hour window.
The health benefits of intermittent fasting and its applicability to many diseases are clear not only from his work but from a growing body of other research too. There are impediments, however, to the widespread adoption of these eating patterns.
“A diet of three meals with snacks every day is so ingrained in our culture that a change in this eating pattern will rarely be contemplated by patients or doctors. The abundance of food and extensive marketing in developed nations are also major hurdles to be overcome."
However, the tide might be turning. “An increasing number of physicians are becoming aware of intermittent fasting as a complement to exercise and a healthy diet. Its ability to help people lose weight and reduce their risk for many diseases is prompting some physicians to recommend intermittent fasting to overweight patients and those with insulin resistance or an unhealthy blood lipid profile.
“If the results of clinical trials of intermittent fasting in patients with diabetes, cancers, cardiovascular disease and inflammatory diseases show the benefits of intermittent fasting, then we can expect that intermittent fasting will be prescribed for patients with these diseases. Stay tuned!"
Anneliese Burgess
Co-editorAnneliese Burgess is co-editor of Vrye Weekblad.
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