How Fast Can You Lose Weight Safely?

There are many reasons for wanting to lose weight quickly. Maybe you have a special occasion coming up that you want to get into shape for, or maybe you want to get your health on track as quickly as possible.

While it is possible to speed up your weight loss to achieve your goals quicker, losing weight too quickly can be detrimental to your health. It may even be counterproductive to your goals in the long term.

Read on to discover how to lose weight quickly and safely.

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The physiology of weight loss

The physiology behind losing weight is complex, and there are multiple factors at play. Put simply, it comes down to creating a calorie deficit. To lose weight, you need to consistently consume fewer calories than you burn each day over a certain period of time.

Three are three factors that affect how many calories you burn each day:

  1. Resting metabolic rate — The number of calories that your body burns just to maintain normal bodily functions.

  2. The thermic effect of food —The energy required to digest food.

  3. Thermic effect of activity The amount of energy you burn performing daily activities, such as cleaning the house, carrying groceries, exercising, or even fidgeting.

In order to lose weight, you need to create a negative calorie balance. You can do this by either decreasing the amount of calories you eat or increasing the amount of calories you burn.

Age and gender are two additional factors that affect your resting metabolic rate and your daily caloric needs.


Lean muscle mass consumes more calories at rest than fat does. This means that the higher your ratio of lean muscle mass to fat, the more calories you will burn while resting and relaxing.

Lean muscle mass tends to decline with age at an average of around 3-8% per decade after the age of 30,¹ causing a decrease in resting metabolic rate. Studies have shown that this decrease is not only due to a reduction in lean muscle mass, but it is also likely due to the reduced metabolic rate of individual organs as you age.² ³

Maintaining muscle mass as you age will slow down the decline in your resting metabolic rate. While you won’t be able to preserve the metabolism of your twenties, for example, by keeping fit and active, you can boost your metabolism as you get older. Overall, as you age, it will take you longer to lose the same amount of weight than it did when you were younger.


Gender also plays a role in how quickly you can lose weight. As with age, this is related to body composition and the ratio of muscle to fat in your body.

Men have a different body composition to women. On average, muscle in men makes up 38.4% of their body weight, whereas women tend to make up 30.6% of their total body weight.⁴

The result of this is that men typically have higher resting metabolic rates than women, allowing them to lose weight more quickly if they consume the same number of calories.⁵

A study that examined the differences in rapid weight loss between men and women found that the composition of weight loss was different between the two genders. Men were found to have lost almost double the amount of fat-free mass as women over the same period. This has implications for weight loss because muscle is more metabolically active than fat tissue.⁶

How does a calorie deficit result in weight loss?

In theory, you need to burn 3,500 more calories than you consume each week to lose one pound of body weight. This amounts to reducing your calorie intake by 500 calories per day for a week.

However, this formula is far too simple as it doesn’t take into account many of the metabolic changes that occur in response to weight loss. It also presumes that you are losing only fat, and that you will continue to lose weight at a steady rate.

The reality is that when you are consuming an energy-restricted diet, you can lose muscle mass as well as fat, which then slows your resting metabolic rate. This decreases the rate at which you can lose weight in the longer term.

How quickly can you safely lose weight?

Guidelines suggest that aiming for a 10% reduction of your initial body weight over six months is a reasonable weight loss goal. After six months, the rate of weight loss usually declines, and you are likely to experience a plateau because your energy expenditure is lower when you have a lower body weight.⁷

If you are overweight (BMI of 27-35), you could aim to lose half a pound of weight per week, whereas if you are obese (BMI over 35) your goal could be to loss one to two pounds per week.⁷

Remember that weight loss is not linear. When you start to lose weight, it can feel quicker and easier, but the rate at which you lose weight will slow after the first several weeks.⁸

Is it dangerous to lose weight too quickly?

Not only can restricting your calories too dramatically set yourself up for failure, but losing weight too rapidly also cause adverse, even dangerous health effects.

Adverse effects of rapid weight loss and/or an overly restrictive diet include:⁹ ¹⁰

  • Dehydration

  • Risk of gallstones requiring hospitalisation or surgery

  • Nutritional deficiencies leading to hair loss, brittle nails, fatigue, cramps, muscle weakness, and lowered immunity

  • Muscle atrophy (loss)

How to speed up healthy weight loss

In the long term, losing weight quickly may not be the best option. It may be more beneficial to aim for a slower, more sustainable weight loss that maintains or builds lean muscle mass at the same time as losing fat.¹¹

Maintaining muscle mass while losing fat ensures that you maintain your resting metabolic rate, rather than decreasing it. You can help to preserve your metabolic rate by incorporating regular exercise, especially strength training, into your weight loss program and ensuring you consume adequate protein.¹²

The lowdown

While it is possible to lose weight quickly, losing weight too fast can be counterproductive to your overall weight loss goals. If you are looking to lose weight, it is recommended that you aim to lose 10% of your body weight over a period of six months, or a maximum of 1% per week.

While it is common to start seeing results soon after you start a weight loss program, remember that weight loss is not linear. Your weight loss may naturally slow down as your body weight drops and your resting metabolic rate is lowered. To maintain your metabolic rate, make sure to exercise regularly and consume enough protein.

When it comes to weight loss, slower may well be better for lasting results.

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