What is fasting?
There are many different regimes for fasting. We all fast overnight for 6-8 hours when we are asleep, hence ‘break-fast’ is what we call the first meal of the day. So some people like to ‘fast’ by extending this natural time of fasting by not having a meal first thing in the morning and breaking that fast at mid morning or even lunchtime. This is sometimes referred to as Time Restricted Eating, i.e. only eating in a 8-10 hour window. There is also the fasting of the 5:2 variety where for 5 days of the week you eat normally and for 2 days you only eat around 25% of your normal intake. More info can be found on the BHF website.
You could also do this every other day, or restrict the window for eating right down to only 6 hours. This of course is much more restrictive and difficult to do.
Also bear in mind that this is not just food but drink as well. You can drink water and black tea/coffee (with no sugar of course) but anything else will have a calorie value and therefore break the fast.
Should I fast for weight loss?
There is a likelihood that if you are reducing the time during the day (or week) that you actually consume food or drink then you may be overall reducing the amount of calories you consume which can lead to weight loss. But like any nutrition regime, if you stop doing it, the weight is likely to go back on. So it’s important to find a routine that you can stick to forever.
Should I fast for overall health?
There is increasing evidence that our gut health plays a major role in our overall health. From reducing anxiety to a reduction in body wide inflammation and improving overall energy to reducing risk of cancer, stroke and dementia among many others. One way to improve your gut health is to give your gut a break. So not consuming food/drink for an extended period up to (15 hours) can help its natural repair mechanisms, so improving gut health.
How long should I fast?
We are all different so what works for one, might not work for others. Try a variety of different ways of fasting, as above, and just see what works for you. It’s important to make sure that it is something you can build into your every day life for years/decades hopefully to come. See how you feel on different regimes. Do you feel energised? Or does it make you feel irritated and tired? Is your body responding positively? Losing weight, less digestive issues etc? Or feeling bloated, gaining unwanted weight? Can you maintain it? Or is it a real effort so can only be done short term?
Is it OK to exercise on an empty stomach?
This is also highly personal. Some people can only exercise on an empty stomach and some can eat a big meal and immediately go do a workout. If you can train in a fasted state and feel fine then great, go ahead. If it just doesn’t work for you then a small snack half to one hour before might be better.
Men vs Women
As for which is best for weight loss, there was a study done years ago that found that men lost more body fat by training fasted and that women gained more body fat doing the same thing. But it was only one small study and I don’t think it took into account where those women were on their cycle or if they were peri menopausal or menopausal. And of course, historically all these types of studies are done on men so we really don’t know how it affects women most of the time. So my advice would be to see how you feel and see what happens!