Oct 30, 2021 / by Jon Bellis / No Comments

We’ve all heard of yo-yo dieting, but what is it? It’s when you lose weight, only to put it all back on again.

That’s not so bad, you might think. If you put it back on, you can always take it off again. After all, you’ve done it once; you can do it again.

Well, it doesn’t work like that in practice. Repeated weight loss and weight regain will leave you in a worse state than when you started. And you’ll find it harder and harder to take the weight off.

In this post, we’ll explain why you should avoid yo-yo-dieting and how to combat it. Read on to find out more.


A quick quiz

Let’s start with a quiz. Which of these foods will make you gain weight?


Close up of icing sprinkles doughnut. Avoid these if you want to avoid yo-yo dieting


A close up of different types of berries. No need to avoid these


A pat of butter. Minimise if you want to avoid yo-yo dieting


A sponge cake. Avoid these if you want to avoid yo-yo dieting


A big collection of different types of carbs. No need to avoid these if you want to avoid yo-yo dieting


Close up of broccoli. This is a good choice if you want to avoid yo-yo dieting

And the answer is none of them! And all of them! Yes, I’m being deliberately befuddling. At a fundamental level, it’s not what you eat that matters for weight gain, but how much of it. It’s possible to gain weight with all these foods if you eat enough of them.

As you’ll see later, there’s more to it than that. There has to be, or why would health practitioners tell you to limit foods like cake? More on that further down.


The law of weight loss

But for now, let’s turn this observation into something practical. I call it the law of weight loss because it’s so fundamentally true. It’s basically this: you will gain weight if you consume more calories than you burn. On the flip side, you’ll lose weight if you consume fewer calories than you burn. We might write it like this


Gain weight: calories in > calories out


Lose weight: calories in < calories out


Here, ‘calories in’ is your food and drink intake, and ‘calories out’ is your calorie burn. The following is also true: if you consume the same number of calories as you burn, you’ll stay the same weight.


Calorie equivalence

So, let’s imagine you burn 2000 calories a day. You can eat 2000 calories worth of food without putting on weight. That’s

Six icing sprinkles doughnuts

Six doughnuts


22 heads of broccoli. That’s heads, not florets!

Twenty two heads of broccoli


Now, remember we said that there’s more to it than that? The answer to this next question will give you a clue. Realistically, which do you think you’d more likely be able to chow down in 24 hours?

More on that later. But for now, remember that if you burn 2000 calories, you can have six doughnuts in 24 hours without gaining weight. Hold that thought.


Body compartments and weight loss

Now let’s move on and talk about body composition. In the weight loss industry, we talk about fat mass (FM) and fat-free mass (FFM). Fat-free mass consists of everything except fat – bones, organs, muscles and so on.

Fat mass and fat free mass

When you lose weight, which part do you think you lose?

In fact, you could lose a significant amount of fat-free mass. Up to 30% of your lost weight could be lean tissue, especially if you lose weight quickly.

Now you might think that’s ok because you won’t need as much muscle to carry around your lighter self. Perhaps your power-to-weight ratio improves despite lost muscle?


Weight regain and lean body mass

But consider two points on this. First, wouldn’t it be better to keep hold of your muscle when you lose weight. Think how much more capable you’d be. Second, what happens if you gain weight again? Would you gain back the muscle you lost?

The answer turns out to be no.

When you gain weight, you don’t gain muscle to the same extent that you lose muscle when you lose weight. Instead, you tend to gain more fat and less muscle. There is even evidence that you may grow new fat cells in response to weight regain. That means you can end up back at the same weight, but with more fat and less muscle. This is especially true for rapid weight loss and large calorie deficits.

What happens if you do this repeatedly, so-called yo-yo dieting? You’ll gradually lose muscle and gain fat. That’s a great reason to avoid yo-yo dieting.


A comparison of two weight loss approaches

At this point, let me introduce you to two twins, A and B. Let’s call them Agatha and Beatrice. Agatha is going to lose weight but do everything she can to retain her muscle. And when she gains weight, she’s going to do everything she can to gain muscle. On the other hand, Beatrice is going to pay no attention to muscle; she’s just going to focus on weight.

Look what happens to their respective body compositions when they lose and regain the weight. Neither Agatha nor Beatrice avoid yo-yo-dieting. But Agatha ends up with more muscle and less fat, while Beatrice has less muscle and more fat.


Weight cycling with weight training.



Weight cycling without weight lifting

Preserving lean body mass

So, what has Agatha done differently to Beatrice? She’s lifted weights and prioritised protein in her diet. Some of our clients actually gain muscle while they lose weight, but typically for those who lose weight rapidly, they may lose 10% of their lost weight as muscle, rather than 30%. So, I’ve conservatively assumed Agatha loses 10% of her lost weight as muscle.

When you gain weight, it’s a lot easier to put on muscle. Our clients who want to put on size will typically gain 3-4 kg of muscle with even a modest calorie surplus and weight gain. Bodybuilders will also tend to gain weight to gain muscle and then try to retain it as they lose body fat for a show. Again, I’ve conservatively assumed a more modest muscle gain for Agatha.

Even so, she is able to gain muscle with every successive weight cycle.


Do you yo-yo diet?

You might be untroubled by the thought that weight cycling makes you gain fat and lose muscle. After all, it doesn’t apply to you because you avoid yo-yo dieting. Are you sure? Do you not gain weight at Christmas or on your summer holiday, only to take it off again?

Or perhaps you like to diet during the week and go to town at the weekend? It may only be a pound or two, but it’s still a weight cycle; it’s just a mini weight cycle occurring 52 times a year. Although all the weight cycling research focuses on rapid weight loss and regain, it makes sense that weekly cycling would be detrimental to your body composition.


Why is muscle important?

Why are we so focused on muscle? Does it really matter? You bet it matters! For a start, you won’t be happy with the way you look, and without the muscle tone, your posture will deteriorate. In fact, there are many reasons why muscle is essential.

But the feature of muscle that is most relevant to this discussion is that muscle burns calories, even when you’re not using it.


Resting Metabolic Rate

Your Resting Metabolic Rate (RMR) is the number of calories you burn in 24 hours of … doing nothing. Your heart, brain, liver, kidneys and other organs all take a share of your RMR. But so too does muscle; typically around 20% of it, even when you are inactive. So, the more muscle you have, the higher your RMR and the more calories you will burn.

That’s great news if you like your food because it will enable you to eat more before you start gaining weight.


The real consequence of weight cycling

Let’s go back to our twins Agatha and Beatrice. Agatha has an RMR of 2000 calories and can have two doughnuts for breakfast, two for lunch and two for dinner. In contrast, if Beatrice has six doughnuts a day, she will gain weight because her RMR has been reduced by weight cycling and now stands at 1784 calories a day.

So, Beatrice has a calorie excess of 216 calories a day or 78,840 per year. Assuming a pound of fat equates to 3500 calories, that’s the equivalent of 22lbs of fat per year.

Now, it’s more complex than that, as you can imagine. For a start, people have willpower! But there is definitely an upward pressure exerted on your weight by a lowered RMR.


The wrap-up

So, what’s the moral of the story? No, it’s not to avoid yo-yo dieting. That can be good for your body composition under the right circumstances. No, the moral of the story is to lift weights; lift weight, lose weight, feel great, as we like to say.

Before we close this discussion, let’s be clear, doughnuts are not good food! They are not healthy or filling. You’d get pretty hungry if all you ate were doughnuts. And you’d become unwell fairly quickly too. Nor is it beneficial to eat nothing but broccoli, even if you could chow down 22 heads a day.

The secret to healthy weight loss is to get as much variety as possible whilst ensuring your food is filling and nutritious. You’ll need to get plenty of protein, fibre, liquid and healthy slow-digesting carbs.


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