It doesn't matter what high-protein diet you're following. What matters is that on average you finish the day in a calorie deficit; eating fewer calories than you burn. Because that's what'll allow you to lose weight consistently and effectively. It's the best-known way for men to lose their belly fat and a fool-proof strategy to achieve weight loss for women.

Here's why most people fail on their diets. They say: "Ok, I'm sick of being overweight. From tomorrow I'm eating only vegetables, no junk food, cutting out drinking, and getting a PT, and running 2km a day. Pass me my water bottle!"

Everyone tries to do TOO MUCH, thus suffering mentally and physically and forgoing focus on what really matters: a CONSISTENT deficit of daily calories. An overkill leads to lack of consistency and lack of motivation. This almost always ends in failure.

How much of a calorie deficit do I need to lose weight?

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Research shows diets are very effective when subjects are in a daily calorie deficit of 500 calories (1). This is because a cumulative deficit of 3500 calories is required to achieve a pound of body weight loss (approximately half a kilo) (2).

This means a deficit of 7,700 calories equates roughly to a kilogram of body weight lost (2).

So you'd need to eat in a 500 calorie deficit for 15.4 days to lose a kilogram of fat (2).

Here's a real-world example of such: let's say Tina burns 2000 calories per day (known as her Total Daily Energy Expenditure or TDEE), and thus plans to eat a 500 calorie deficit daily.

Tina would eat 1500 calories per day, and her week would look like this:

Monday = deficit of 500 calories

Tuesday = deficit of 500 calories

Wednesday = deficit of 500 calories

Thursday = deficit of 500 calories

Friday = deficit of 500 calories

Saturday = deficit of 500 calories

Sunday = deficit of 500 calories

TOTAL DEFICIT = 3500 calories.

So by the end of the week, Tina would have lost roughly 1 pound or a half a kilo. If Tina does this for 2 weeks consecutively (15.4 days to be precise), she's basically lost 1 kilogram of fat.

Whilst the notion that a "3500 calorie deficit equates to a lost pound of body fat" is sometimes seen as an oversimplification (3), it's still a strong yardstick for us to use. This is because Tina could experience some muscle loss, thus making the equation not totally accurate. But for the sake of simplicity, this is what weight-loss experts and nutritionists continue to use (2).

But for Tina, her 500 calorie deficit actually equates to a 25% calorie deficit. This walks the line between the "moderate deficit" category and the "large deficit" of dieting (4):

Small deficit: 10-15% below daily activity

In this case, Tina would reduce calories by 200-300 calories daily.

Moderate deficit: 20-25% below daily activity 

In this case, Tina would reduce calories by 400-500 calories daily.

Large deficit dieting: 25% below activity of greater

In this case, Tina would reduce calories by 500 calories or more.

So depending on how large you are, and how much body fat you have to lose, the 500 calorie deficit can be an aggressive one if you're Tina, but not as much if you burn 6000 calories per day due to being significantly overweight.

When you're planning a weight loss diet, you'll decide which deficit from the above you want, depending on how quickly you want to lose weight. And of course the bigger your deficit the harder it is to maintain. That's why many people start diets in the "small deficit" category, to ensure dietary adherance.

So now you know how large your deficit needs to be in order to lose weight. Now all you need to discover is how to calculate how many calories you burn (TDEE) and subtract that from there.

Weight loss for men and women: Working out your calorie deficit to lose belly fat

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As mentioned, the term "Total Daily Energy Expenditure" (TDEE) refers to how many calories you burn daily. In the aforementioned example of Tina, her TDEE was 2000 calories.

You can work out your TDEE by utilising the four steps below:

Step 1 = Work out your Basal Metabolic rate (BMR). This is the number of calories your body needs to stay alive for organ functioning. You'll work out your BMR by multiplying your body weight by 20.

For example, Jason is 110 kg.

110 kg x 20 = BMR of 2200 calories.

Step 2 = Work out the Thermic Effect of Feeding (TEF). This is the number of calories you burn daily from the food you eat, given the energy generated by the body to digest it. So simply multiply your BMR by 0.1 to get the TEF.

Jason's BMR = 2200 calories.

2200 calories x 0.1 = 220 TEF

2200 BMR + 220 TEF = 2420 calories so far.

Step 3 = Work out the Exercise Energy Expenditure (EEE), which is how many calories you burn during exercise. This is basically impossible to get completely correct, but generally, an hour of light exercise is around 250 calories burned, and an hour of intense exercise (training legs, for example) is about 500 calories burned per hour.

Let's say Jason is doing resistance training 5 times per week. We'd add on 500 calories.

2200 BMR + 220 TEF + 500 EEE = 2920 calories.

Step 4 = Work out your Non-Exercise Activity Thermogenesis (NEAT). This is the number of calories you burn daily away from exercising. It's things like maintaining posture sitting at your desk, chewing gum, and walking to the bathroom.

Desk job employee = 250 calories from NEAT

A parking inspector, delivery driver, building site worker, etc = 500 calories from NEAT

Let's say Jason has a desk job. Our numbers now look like this:

2200 BMR + 220 TEF + 500 EEE + 250 NEAT = 3170 calories.

Jason's TDEE is 3170 calories.

So now, Jason must decide how aggressive he wants to approach his weight loss. Let's say he aims for a moderate deficit of 20%, then he'd simply reduce that from his TDEE.

20% of 3170 calories is 634 calories.

3170 calories - 634 calories = 2536 calories.

Therefore, Jason needs to eat 2536 calories per day to lose weight at a moderate deficit of 20%.

And you can see why the "500 calorie a day deficit" is a good starting point, but in the case of Jason, a 20% calorie deficit worked out to be significantly more than Tina, at 634 calories per day.

And based on these numbers, if Jason can stay consistent, he'll lose (roughly) a kilogram of body fat after 12.1 days!

Now in terms of how Jason sets up his diet plan, is beyond the scope of this article. However, your TDEE is a powerful piece of knowledge to have as you push towards your fat loss goals!

I hope this article helps you understand the levels of efficiency of various calorie deficits, how to set yours, and roughly how long it will take you to achieve your fat loss goal.

All the best torching the fat!

References

(1) Carels RA, Young KM, Coit C, Clayton AM, Spencer A, Hobbs M. Can following the caloric restriction recommendations from the Dietary Guidelines for Americans help individuals lose weight? Eat Behav. 2008 Aug;9(3):328-35. doi: 10.1016/j.eatbeh.2007.12.003. Epub 2008 Jan 4. PMID: 18549992.

(2) Hall KD. What is the required energy deficit per unit weight loss?. Int J Obes (Lond). 2008;32(3):573-576. doi:10.1038/sj.ijo.0803720

(3) McArdle WD. Exercise physiology: energy, nutrition, and human performance. 4th edition edn. Williams & Wilkins; Baltimore: 1996.

(4) McDonald, L. 2008. Body Recomposition: Setting the Deficit – Small, Moderate or Large.