intermittent fasting
Intermittent fasting (IF) has gained a lot of popularity over the recent years and unlike most other trends that are short-lived, intermittent fasters say it’s a lifestyle that’s here to stay. Whether that’s true or not, time will tell, but for now let’s look at the science.
What is IF:
IF can be done in a few ways:
· 5:2 diet when you fast for 2 days / week
· Alternate day fasting
· Time-restricted fasting, e.g. 16h fast & 8h eating window
The way fasting works is that when there is a limited intake of food, the body saves glucose (the main source of energy in the body) for the brain and other essential organs and functions. For everything else, the body’s fat stores are used. However, similar metabolic changes can also be achieved by every restricting your energy intake to ~500 kcal/day.
After 24-36h the body enters starvation mode, which involves an increased protein catabolism (the body draws protein from muscles) and gives the body a bit of a shock, because it doesn’t know whether you’re starving for fun or because you’re actually starving and there is no food available. This may mean that you’re losing your muscle mass, which is key for healthy ageing. It also means that the next time you eat, your body is going to extract and absorb a lot more from a meal than it would normally and hold onto it tight, because it doesn’t know when the next “famine” is coming. All of this for no extra benefit from extended fasting! The same concept applies to chronic dieting, which involves severe under-eating.
Research:
Most of the research to date is done in mice, which cannot be extended to humans. It can only give a hint that it may be worth doing more research in humans. Very few studies have been done in humans, which means that in research terms IF is still a baby and we still don’t know a lot about it.
With regards to weight loss, IF is only effective if there is a calorie deficit. This works exactly the same way as any other diet. Once you’re off it and the calorie deficit is eliminated, the weight comes back on. Therefore, it’s only a short-term solution.
More exciting research is showing that there may be some benefits for cardiovascular disease and type II diabetes. This is due to increased insulin sensitivity (good for diabetes management) and more efficient fat clearing from the blood after a meal (an important cardiovascular risk factor). Also, having early dinners (fasting in the second half of the day) shows improvements for type II diabetes. So the saying that one shouldn’t eat after 6pm perhaps is not a bad one? BUT despite these positive hints, results are still mixed and more research is needed.
Important Factors to Consider:
1. Does fasting make you think of food more than you normally would?
2. Do you get really hungry and can’t wait for your next meal?
3. Do you feel guilty if you break your fast before you’re meant to?
4. Do you tend to overeat because you’ve waited too long to have food or because you think you need to eat more because you won’t be able to eat for a while?
5. Are you avoiding social gatherings because you’re fasting?
6. What does your diet look like when you’re not fasting? Are your cravings more exaggerated? Do you lose control around food?
If you answered “yes” to any of these questions, it may mean that IF is causing disordered eating patterns to develop or exacerbating existing ones. We don’t want any obsessive behaviour around food and if you feel that might be the case, IF is not for you. Respecting your body is one of the most important health tips you’ll ever get from me.
Implications for Women:
A study showed that alternate day fasting negatively affects glucose tolerance (how high your blood sugar goes up after a meal and how long it stays up) for women, but not for men. This was only a 1 small study, so more research is needed to confirm it, but the hint is there.
Also, when energy intake is low for a prolonged period of time, the hypothalamus (part of the brain) is affected, which might in turn affect the release of gonadotropin releasing hormone (GnRH), as it is released from the hypothalamus. Normally, GnRH signals to the pituitary gland to release luteinising hormone (LH) and follicle stimulating hormone (FSH), which act on the ovaries and trigger the production of oestrogen and progesterone. When this chain of processes is disturbed, women are at risk of irregular or missing periods (hypothalamic amenorrhea), infertility and reduced bone health (risk of osteoporosis - when bone mass density decreases).
This does not mean that IF is unsuitable to women, but it does mean that women should not over-stretch themselves with fasting and stick to the lower end of the spectrum (12-16h fasting), which is essentially an overnight fast with an early dinner / later breakfast. For example, dinner at 6-7pm - breakfast at 8-9am or dinner 8-9pm - breakfast 10-11am.
Mixed feelings:
Like everything else food-related, IF works differently on an individual basis. For example, some report gaining mental clarity and increased focus, while others suffer from headaches and decreased concentration.
If you're interested in trying IF, start with a shorter fasting window and work it up. BUT...
Be Aware:
· IF is not recommended for people with a history of eating disorders, disordered eating, or to those who might be prone to it
· IF is not recommended for pregnant women
· People with health concerns must consult their doctor if interested in trying IF
· Diabetics must work with clinicians in case of low blood sugar
· Be aware that personal trainers and other IF fans may have been reading blogs (not research), Instagram posts (not research), hearing it from their peers (not research), and studies on mice (at its best)
