Intermittent Fasting

Intermittent Fasting: what is it?

Intermittent fasting is the clearest example in nutrition of a method being mistaken for a mechanism. It works for a lot of people, and the reason it works is usually straightforward: compressing eating into a shorter window cuts out a meal and an evening of snacking, so intake falls. That is a legitimate and useful tool. It is just not a separate route to fat loss that bypasses energy balance.

The common protocols

All of these are ways of arranging the same weekly calorie total. None of them is inherently superior; they differ in how well they fit a given life.

Who it suits, and who it does not

It suits clients who are not hungry in the morning, who prefer fewer and larger meals, who like a simple rule better than tracking, and whose training sits comfortably inside the eating window. For those people it removes decisions, which is often the whole benefit.

It suits far less well the client who trains early in the morning, whose job involves physical work before noon, who gets irritable and unfocused when fasted, or who struggles to reach a high protein target. Compressing 2.0 g per kilogram of protein into two meals is genuinely difficult for a larger client.

The claims worth being careful with

Fasting is frequently sold with claims about autophagy, hormone optimisation and metabolic transformation. Some of these mechanisms are real areas of research, and the honest position for a coach is that the reliable, demonstrated benefit for a general client is easier calorie control, not a documented metabolic advantage over the same calories eaten across more meals.

A specific caution: clients with a history of disordered eating, clients who are pregnant, and clients managing diabetes or on medication that requires food should not be steered into fasting protocols by a personal trainer. Those are medical conversations. Recognising the boundary is part of the job.

• Fasting controls when, not how much; calories still decide the outcome.
• Check that protein is reachable inside the eating window before prescribing it.
• Place the eating window so training sits inside it or just after it.
• Refer rather than adapt when there is a medical or disordered-eating history.

How to set it up with a client

Start wider than the target. A client going straight from breakfast at seven to a first meal at one will have a miserable week. Moving the first meal later in stages over two or three weeks makes the transition almost unremarkable.

Then check the practical things: is the protein target still reachable, does training land in a sensible place, and does the eating window survive family dinners and work travel. A protocol that collapses every weekend is not a protocol, and at that point the client is better served by a normal three-meal structure with a calorie target.