How Fast Should You Lose Weight?

Yes, I know. You want to lose weight like yesterday.

However, I’m going to explain why losing weight a bit more slowly is more beneficial for your progress and wrap things up with some guidelines on sensible weight loss targets. But first, let’s understand the difference between weight loss and fat loss. People conflate the two, but they’re not exactly the same thing.

Weight loss vs fat loss

When we talk about body weight, we’re referring to everything neatly packed inside that meat suit you’re wearing, like bones, skeletal muscle, organs, body fat, water, glycogen, etc.

When we refer to fat loss, we’re only focused on two specific things––body fat and muscle mass. More to the point, the goal of every sensible fat-loss diet is to ensure most––if not all––of the weight you lose comes from body fat while preserving as much muscle as possible.

Retaining muscle during a diet is arguably just as important as losing excess body fat (I’ve explained why in this article if you’re interested).

Alongside the obvious players like high protein intake and resistance training, how quickly you lose weight does seem to impact muscle retention.

How does the rate of loss impact muscle retention?

For example, Garthe and colleagues compared changes in body composition and strength in elite athletes during fast (1.4% of body weight/wk) or slow (0.7% of body weight/wk) weight loss. 1 Effect of two different weight-loss rates on body composition and strength and power-related performance in elite athletes, Garthe I et al. 2011

Both groups lost about 4kg (~9 lbs) of body weight, but the slow group gained 1 kg (~2 lbs) of muscle, while the fast group lost about 0.3 kg (~0.7 lbs) of muscle.

In another study by Mero et al. (2010), normal-weight women were randomised into two groups: 2 Moderate energy restriction with high protein diet results in healthier outcome in women

• ‘Fast’: Followed a 1100kcal deficit/day (aiming to lose 1kg/week or roughly ~1.5% of total bw/week)
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• ‘Slow’: Followed a 550kcal deficit/day (aiming to lose 0.5kg/week or roughly ~0.7% of total bw/week)

The fast group lost more body fat, but there were no differences in muscle mass. However, the fast group saw a significant reduction in their bench press strength and reduction in testosterone (30%), with the researchers noting had the study been longer, this could have led to muscle loss, and advised that:

A weight reduction of 0.5 kg per week with ~1.4 g protein/kg/day can be recommended to normal weighted, physically active women instead of a larger (e.g. 1 kg per week) weight reduction, because the latter may lead to a catabolic hormonal state in the body after four weeks.

Finally, a meta-analysis published in 2021 found deficits larger than 500 kcals were associated with increased muscle loss. If you crunch the numbers, this generally translates to a weekly weight loss of about 0.4-0.8% of total bodyweight/week for most people. 3 Energy deficiency impairs resistance training gains in lean mass but not strength: A meta-analysis and meta-regression

Now, you could argue losing weight faster could still be beneficial. You lose body fat faster, maybe lose a little bit of muscle, which likely won’t impact things in the long term since muscle can be regained quickly and get done with the diet sooner, right?

Maybe.

But this argument misses the biggest factor driving results: your ability to adhere to a larger deficit. And, unsurprisingly, the larger the deficit, the harder it is to stick to long enough for fat loss to happen.

Case in point–

In a 2023 study, researchers randomised 14 resistance-trained women into two groups: 4 Efficacy of progressive versus severe energy restriction on body composition and strength in concurrent trained women, Vargas-Molina S et al. 2023

• A ‘severe’ energy deficit: 25 kcals/kg of fat-free mass per day
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• Progressive energy deficit: Starting at 40 kcals/kg of fat-free mass per day, which was reduced by 5 kcals/kg every two weeks until they reached 25 kcals/kg of fat-free mass per day by the end of the study).

By the end of the study, the severe energy restriction group lost less body fat (-1.2 kg) than the progressive energy group (-1.7 kg).

No, the aggressive diet group didn’t break thermodynamics. The explanation was much simpler: They didn’t adhere to the intended deficit. So much so that the progressive energy deficit group had a lower caloric intake compared to the ‘severe’ energy deficit group in weeks 7-8 (table below).

As the researchers note:

Scrutiny of participants’ nutritional records in our study revealed that participants in the SER group did not consume the number of calories proposed (25 kcal·kg−1 FFM). This may help to explain the somewhat lower FM reduction (− 1.2 kg; ES = − 0.20) compared to the PER group (− 1.7 kg; ES = − 0.39), although at the same time it indicates a greater adherence for PER.

This highlights the irony of wanting to lose weight as quickly as possible. In most cases, adherence takes a hit, and people either end up in a smaller deficit than they’d initially intended or find it too difficult to stick to and quit.

So, how quickly should you lose weight?

The general recommendation to maximise fat loss while retaining as much muscle as possible is to set your target rate of loss between 0.5 and 1% of total body weight/week. If you have more fat to lose, aim for the higher end. If you don’t have that much fat to lose, aim for the lower end.

The benefit of using a percentage of your total body weight is the target rate of loss (and the deficit) scale with your weight.

For example, someone who starts a diet weighing 200 lbs aiming to lose 0.5% of total bw/week would aim to lose 1.0 lb/week. On the other hand, someone who weighs 160 lbs and aims to lose 0.5% of total bw/week would aim to lose 0.80 lbs/week.

This method works better than arbitrary numbers like 1-2 lbs/week, which may be too fast or slow for you as an individual.

Tip: When I work with clients, I’ll give them a range for the weekly target loss since this gives them more flexibility with their diet. For example, instead of 0.5%, I’ll set the deficit based on 0.5–0.7% of total body weight/week. If the client knows they have a social engagement coming up on the weekend where it might be harder to stay on top of their nutrition, they can aim for the slightly larger deficit during the week (0.7%) to create a buffer for the weekend. The result is their weekly deficit isn’t impacted too much.

How to establish a caloric deficit based on these percentages

Ok, so you understand how much weight you should aim to lose. But how do you calculate an actual calorie reduction using these percentages? Let’s talk about that next.

Take your body weight and multiply it by your target rate of loss and multiply that by 500 if using pounds or 1100 if using kilograms.

For example, if you weigh 200 lbs and want to lose 0.5% of your total body weight/week:

Determining weekly weight loss (in lbs):

👉 200 (lbs)*0.005 = 1.00 lb/wk (i.e., your target weight loss is one pound per week)

Determining the calorie deficit:

👉 1.00 (lb/wk)*500 = 500 kcals/day (i.e., you’ll need to reduce your caloric intake by 500 from your maintenance intake).

For this example, let’s assume this person’s maintenance intake is 2500 kcals.

👉 2500-500 = 2000 kcals/day.

So, this hypothetical person will need to eat 2000 kcals/day to lose somewhere around 0.5% of their total body weight/week.

Simple.

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