Dietary fibre is the name we use for complex plant based carbohydrate molecules that our intestines are not able to digest. Since we can’t digest fibre, it goes straight through the intestine after we eat it, and comes out the other end. And since it fills up the intestine, it contributes to a feeling a fullness. It can also bind up certain substances, so that they travel through the intestine and come out the other end, rather than being absorbed by the body. In theory, these effects should mean that increased intake of dietary fiber results in weight loss, at least if you’re overweight.
In recent years, one of the most popular diet interventions has been fasting, in a variety of different forms. These have included intermittent fasting diets in which you’re supposed to fast for a few days per week, such as the 5:2 diet, or a few days per month. They’ve also included various forms of time restricted eating, such as the 16:8 diet, where you’re supposed to get all your calories within an eight hour window each day, and the more extreme warrior diet, in which you’re supposed to get all your calories in a four hour window. But there is still little clarity on how effective these modifications are in terms of weight loss. And up to this point, pretty much all the evidence in support of fasting comes from animal studies, which are notoriously unreliable.
Traditional diet advice over the last fifty years, still espoused by most health authorities around the world, holds that if you want to lose weight, you need to cut down your fat intake. In the last few decades, a number of alternative diets have sprung up claiming that you should instead be cutting down your carbohydrate intake. These include the LCHF, Atkins, paleo, and more recently the ketogenic diets. But what do the randomized controlled trials say? Should you cut down on fat or carbs if you want to lose weight?
“Try to cut down on the salt.”
I’m sure many people have gotten this well-meaning piece of advice from their doctor, especially if their blood pressure is a little bit high. It ranks up there with not smoking or drinking alcohol and avoiding red meat, saturated fat, and sugary drinks as one of those things we’re told to do if we don’t want to die prematurely. It is actively promulgated by government health authorities all over the world, including the NHS in the UK and the FDA in the US.