Why Diets Make You Fatter

In this blog, I’m going to talk about diets and why most dieters are actually making themselves fatter and not slimmer…to put simply ‘why diets make you fatter’…

When people go on a diet, they usually starve themselves from the food they love by using willpower. Sooner or later, the dieter will give into temptation and fall off the wagon. During the time on diet, they might have lost weight. In most cases, the weight which is lost is a combination of water, muscle and fat. Losing muscle is the worst thing as it brings down their basal metabolic rate (BMR). BMR is the number of calories a person needs to maintain current weight and function, including breathing, cell repair and a host of other functions we take for granted – the autonomic nervous system. When the dieter concedes to temptation and starts eating the foods that were forbidden they put the weight back plus a few extra pounds. The double whammy here is that the weight gained is almost always fat, which means the dieter has changed their body composition for the worse.

An example, Wendy weighs in at 12 stone (76kg); her body fat is 35% or 26.6kg fat. She decides to go on the latest fad diet and initially loses 4kg of which half is muscle (2kg). After a couple of weeks she gives into to temptation and puts all the weight back plus 1kg. She now weighs in at 77kg (28.6kg being fat) but her body fat percentage has increased from 35% to 37%. If Wendy repeats this cycle of failed yo yo diets she will get fatter and fatter, losing muscle at each cycle and making her likely to suffer from a number of diseases including type 2 diabetes and obesity.

The right way to lose weight (fat)

To lose weight, you have to create a calorie deficit. I have spoken on how to work out your total daily energy expenditure (TDEE) and how to lose fat – create an energy deficit. When losing weight, some of the weight will be muscle – this is unavoidable. However, you can minimise the muscle loss and target the fat loss when losing weight by incorporating the following:

1. Keep up the protein intake and drop the calories through carbohydrates and fats

2. Exercise, preferably resistance training

3. Keep hydrated

4. Don’t reduce calories by too much*

*If you restrict calories by too much the body will go into starvation mode and resist using its fat stores for energy. Studies have shown that keeping your calorie deficit under 500 a day will not prompt this unwanted reaction.

How to work out your Total Daily Energy Expenditure (TDEE)

As a personal trainer, I’m often asked how many calories my clients should be eating every day to lose fat. To do this, we must first work out how many calories an individual requires to maintain their current weight. The Harris Bendict Formula, is the most accurate to date in my opinion.


Harris Benedict Formula

This is a calorie formula using the factors of height, weight, age, and sex to determine basal metabolic rate (BMR). This makes it more accurate than determining calorie needs based on total bodyweight alone. The only variable it does not take into consideration is the amount of lean body mass (muscle). Therefore, it will be very accurate in all but the extremely muscular (it will underestimate caloric needs) and the extremely over fat (it will overestimate caloric needs).

Men: BMR = 66 + (13.7 * weight in kg) + (5 * height in cm) – (6.8 * age)

Women: BMR = 655 + (9.6 * weight in kg) + (1.8 * height in cm) – (4.7 * age)

Note:   1 inch = 2.54 cm

1 kg = 2.2 lbs

1 stone = 14 lbs

For example, Tom is 41 years old, he’s 6’2” tall and weighs 14 stone and 6 lbs. Tom works as a painter and decorator but doesn’t go to the gym (we’ll see why his occupation and exercise regime is relevant soon).

Tom’s BMR = 655 + (13.7 * 91.6kg) + (5 * 188cm) – (6.8 * 41) = 2571

Now that we know Tom’s BMR, we can calculate Total Daily Energy Expenditure (TDEE) by multiplying the BMR by the activity multiplier below:


Activity Multiplier

Sedentary        BMR * 1.2       (little or no exercise, desk job)

Light active     BMR * 1.375   (light exercise/sports 1-3 days/week)

Mod. active     BMR * 1.55     (moderate exercise/sports 3-5 days/week)

Very active      BMR * 1.725   (hard exercise/sports 6-7 days/week)

Extra active     BMR * 1.9       (hard daily exercise/sports physical job)

As Tom works as a painter and decorator but isn’t a gym goer, I’m going to decide he’ll go into the moderate active group (activity factor 1.55).

Tom’s TDEE =  BMR * Activity Multiplier

2571 * 1.55 = 3985 calories/day


Another example, this time using a woman:

Jane is 27 years old, she’s 5’5” tall and weighs 8 stone and 8 lbs. Jane works as a sectary and goes to the gym 3 times a week.

Jane’s BMR = 655 + (9.6 * 54.4kg) + (1.8 * 165 cm) – (4.7 * 27) = 1347

I’m going to decide that Jane’s goes into the light active group (activity factor 1.375)

Jane’s TDEE =  BMR * Activity Multiplier

1347 * 1.375 = 1852 calories/day