The Calorie Formula and Significance of Metabolism

Previously I discussed why calories still matter on Paleo if you have excess body fat to lose. In this post I’ll explain the calorie formula so you can determine roughly how many calories are required per day to lose fat at a fairly steady rate.

How to estimate calorie expenditure

In the past I have always been a calorie counter. I have calculated how many calories I need based on a common formula and then calculated how much of a calorie deficit I would need to lose the target amount of fat. The theory goes that 1 pound of fat contains 3,500 calories which means to lose that fat from your body you need to work up a calorie deficit of 3,500 calories. The numbers work quite well if you work on a weekly basis. 1lb fat loss per week should require a nice round 500 calorie deficit per day.

We start with a calculation which tells us our Basal Metabolic Rate. The metabolic rate is the rate at which the body burns calories. We can use the Harris-Benedict formula to estimate our BMR (do not confuse with the utterly pointless BMI!) based on height, weight and age using this handy online calculator. Note straight away that this does not take body fat percentage into account. This is why I am using it actually, because I am not convinced that I am calculating my body fat accurately. But what this means is that the BMR for a 200 pound athlete will be the same as a 200 pound obese person of the same height and age. Okay so we know this is just an average, let’s move on. Mine comes out at 1,466.

The BMR is how many calories our body needs at complete rest. If you do anything other than lie perfectly still 24/7 you will need to factor in an activity level. Harris-Benedict then give you a chart of various levels of activity and a corresponding multiplier. These are below:

• Sedentary (little or no exercise) : BMR x 1.2
• Lightly active (light exercise/sports 1-3 days/week) : BMR x 1.375
• Moderatetely active (moderate exercise/sports 3-5 days/week) : BMR x 1.55
• Very active (hard exercise/sports 6-7 days a week) : BMR x 1.725

I’ll talk about activity in another post but right now I’d put myself as ‘Lightly active’ giving me a multiplier of 1.375 which now gives me a total estimated calorie expenditure of 2,015.

So you calculate how many calories your body burns per day, then decide how much fat you want to lose, and work out how much deficit you need. Most people want fast fat loss and even 2lbs a week is too slow for many people but let’s look at that for the moment. The average woman requires around 2000-2500 calories a day. I would say that the average overweight inactive woman requires closer to 2000 than 2500 and this is certainly true for me. If she wanted to lose 2lbs per week, she would need a deficit of 1000 calories day bringing her daily allowance to just 1000. This is too low for several reasons.

The Importance of Metabolism

First of all, all we can really do is estimate our calorie needs. We can never calculate it accurately. We just estimated our basal metabolic rate but this varies from person to person. The metabolic rate is the rate at which the body burns calories. People with fast metabolisms (we hate them right?) burn calories very quickly and are generally lean all the time. People with slow metabolisms burn calories more slowly and generally hold on to fat and find it more difficult to shift it.

Unfortunately the calculation used above to estimate it is a one-size-fits-all formula that has no way of accounting for your genetics. Also, recall in the last post that I discussed insulin resistance – someone who is insulin resistant will not process carbs well and will store them as fat. So the BMR is really just a ballpark. Using only the standard calorie formula and ignoring the carbohydrate content of the meals even if our overweight woman managed to stick to 1000 calories, if they come mainly from carbs she’ll be battling hunger and cravings all day long and that simply cannot last.

Our metabolisms are quite clever but they can work against us when we want to lose fat. We are designed for survival and up until fairly recently in evolutionary terms, a big threat to our survival was hunger. Our bodies are designed to conserve energy in times of food scarcity and it does this by slowing down the metabolism so that we don’t need as many calories to live on. This is how people stuck out in remote areas can survive for weeks on very little food – the body will know that it is starving and slow down the metabolism accordingly so that it can function on far fewer calories.

The problem with traditional calorie reduction is that if you take your calories too low you will also trigger the starvation response. Your metabolism will slow down so you don’t need as many calories. Your deficit is not big enough so you stop losing weight. You cut calories some more and this goes on and on but it has it’s limits. Eventually you cannot continue starving yourself and you abandon the diet. But here’s the kicker – the body does not know that this was intentional and it keeps the metabolism low for a while longer after the food returns to normal. You’re now gorging on anything in sight as you’re so fed up of being hungry all the time but your body is still in starvation mode with metabolism at rock bottom so you gain even more weight. 3 months later you go on another diet to lose the weight regained. Classic yo-yo dieting!

Keeping your carbs low and eating enough to get a healthy amount of protein (covered in the next section) & fat and enough overal food in general will allow you to lose fat without hunger pangs or cravings. If you’re hungry you’re either eating too many carbs, not having enough protein or fat or just not eating enough food overall. Many women in particular starve themselves and do not eat enough – their metabolisms are very low and their bodies do not get anywhere near the nutrients they need.

Muscle, Metabolism & Protein

Why is it that a 200lbs athlete needs more calories than a 200lb obese person? Because muscle requires lots of calories to sustain it. If I recall it is something like 50 calories a day per 1lb of muscle. Thus if you were to increase your lean muscle mass by 5lbs, you’d burn around 250 calories a day more without changing your activity level. Of course, you’d need to do some exercise to build the muscle in the first place but you can see why building or at least preserving the muscle you have is so damn important.

Something to add to the starvation response – when your body needs energy quickly it cannot metabolize your stored body fat fast enough so it burns glucose. Once the glucose in your bloodstream has been depleted it will eat into your lean muscle tissue – ouch! Following a severe calories restriction then not only brings your metabolism down but it also lowers your muscle so even when you go back to eating ‘normally’, your body no longer needs as many calories as before to sustain it and thus if you eat the same as you did before, you’ll now put on even more weight! Nasty stuff.

To build muscle generally requires a calorie surpluss alongside a healthy dose of strength training so it does not usually go hand in hand with fat loss that requires a calorie deficit. However you can at least preserve the muscle you do have. Firstly, do not starve yourself. Eat well, do not go hungry and ensure you have adequate protein. Mark Sisson recommends 0.7 – 1g protein per day per pound of lean body mass. If you don’t know your lean body mass use 0.5-0.7lb of body weight. So I weigh currently 166 lbs, I would want between 83 and 116g protein a day. I get that so that’s all good.

Secondly, do strength training – this triggers the muscle fibres and even if there is not enough nutrients to build much more muscle because you’re in a calorie deficit it sends the signals to the body that this muscle is required and it is less likely to be burned. If you are keeping your carbs low then you shouldn’t burn lean muscle anyway but if you do your strength training as well you should most certainly be able to hang on to what you have and maybe build a little as well.

 Remember, this is an estimate

I have not yet talked about activity – I’ll cover that in another post but there are also others factors that determine calorie expentidure. I already talked about differences in genetics, the effect of muscle of calorie consumption but there are other factors such as the thermic value of food, exercise afterburn, effects of sleep and stress etc. I won’t bother discussing these as they are all very well documented in books such as the Primal Blueprint. The point is that these online calculators give you an estimate to start from but at the end of the day it is your results that matter.

You can use a clalculator to estimate your calorie expenditure and then use calculators to estimate your consumption and hopefully you’ll do it right and burn fat at an acceptable level but if it’s not working then you must change something. Your genetics may suck – if you come from a family of overweight people then they probably do but that does not make the calculators wrong! It just means you need to put in a bit more effort than the lucky ones! Remember do NOT starve yourself! Whatever your genetics, eat enough to satisfy all hunger and cravings and then you’ll need to factor in some exercise which I’ll discuss in another post.

I believe that if we eat well and do at least a moderate amount of exercise, everybody should be able to lose fat but the one variable will be the rate at which it comes off. If you don’t have much time for exercise and you have unluckily genetics then you may struggle to lose even 1lb a week where somebody else is dropping 2 or 3 lbs a week. This is life, suck it up and carry on! This is exactly the situation I find myself in right now so I know I need to make changes to see the results that I want.