7 Things you need to know about calories and weight loss

1. What are calories?

Calories are units of energy that allow our bodies to function, from breathing to bicep curls! Every cell in our bodies require energy to function in its optimal, everyday state. Without sufficient calories we are unable to nourish our body correctly which can cause our bodies to adjust to this new, lower level of sustenance, very clever!

2. What is BMR?

Basal metabolic rate (BMR) is the number of calories you burn a day as your body performs basic life sustaining function. From breathing, blood circulation, nutrient processing to cell production.

Your BMR is determined by your sex, weight, height, age, ethnicity, weight history and body composition as well as genetic factors. From these, you have control over your weight and body composition and so creating a calorie deficit allows you to actively alter your BMR.

3. What is TDEE and how is it linked to BMR?

Total daily energy expenditure (TDEE) (otherwise known as maintenance) is your BMR + the average amount of calories that you expend throughout the day doing your daily activities (e.g. walking, shopping, cleaning the house, doing sports etc) – so this is where the national guidelines of consuming 2,500 calories a day for a man and 2,000 a day for a woman come from.

However, these guidelines are very general and actual nutritional intake requirements are highly variable from individual to individual.

4. What is a calorie deficit and how is it related to weight loss?

A calorie deficit occurs when the number of calories a person consumes in a day is smaller than the number of calories they burn. This is a lower amount than the TDEE. Being in a sustained calorie deficit will cause you to lose weight over time.

5. If my weight loss has plateaued is my body in 'starvation mode'?

Starvation mode is your body’s natural response to long-term calorie restriction.

It involves the body reducing calorie expenditure to maintain energy and prevent starvation.

I’m sure you’ve heard it before, ‘if you cut your calories back too much, your body goes into starvation mode and clings onto every calorie making you gain fat and causing you to stop losing weight’.

This isn’t really true.

While it is true that starvation mode exists, it is fairly rare and only occurs to extremely malnourished individuals who have burned all their fat away and are now burning away their muscle mass.

This tends to be when actual starvation mode occurs. However, for the average individual in an extreme calorie deficit, the most probable explanation for a plateau in weight loss is metabolic slowing.

This is different to starvation mode. It is when the body reduces calorie expenditure to maintain energy and prevent further loss of muscle and fat.

This is when weight loss can plateau and people become frustrated with the scales, ditch the diet and gain the weight back – the yo-yo dieting trap. This is why it isn’t advised to try and lose more than 1kg a week, anything more is considered extreme and prompts this sort of response from the body making weight loss ‘ineffective’.

Summary - if your weight loss has slowed down to a halt, your body probably isn't in starvation mode. It has just adapted to your new lower caloric intake and so it isn't using as many calories as it did before, meaning you're not in as much of a deficit as you think you are and so not losing so much weight.

6. How many calories in a lb of body fat?

Per 1lb of body fat there are roughly 3,500 calories. So how many calories do I need to eat to lose weight?

7. How many calories do I need to eat to lose weight?

You may think to burn 1lb of fat a week I must be in a deficit of 500 calories a day right?

Well, not necessarily.

There are more factors at play during fat loss. If you cut back on 3,500 calories a week, yes you will lose weight. But when I say weight, I don’t just mean fat. I mean a combination of fat, lean muscle tissue and water.

This is why it is important when trying to lose fat to supplement a calorie deficit with resistance training and a high protein intake (0.8-1g of protein per lb of body weight) to try and retain, and even in some cases, build muscle. This is a way of isolating ‘general weight loss’ to as close to pure 'fat loss’ as possible.