Low-Fat or Low-Carb: Which Is Best For Weight Loss?

Should my diet be low-fat or low-carb?

That’s a question I’m often asked by people trying to lose weight.

Here’s what the research actually says about dieting…

Work out how many calories you need per day to lose weight and set your protein at an appropriate level. Whether you get the rest of your calories predominantly from fat or carbs doesn’t seem to matter.

The beauty of that is it leaves the door open to be incredibly flexible with your diet. In other words, there is not one best solution.

Let’s look at an example to see how it works out.

All you need to understand is that 1 gram of carbohydrate contains 4 calories, 1 gram of protein contains 4 calories, and 1 gram of fat contains 9 calories.

We’ll use the example of a 70kg woman who wants to lose a bit of weight. Taking her activity levels into account, let’s say we’ve worked out that she needs to take in 1700 calories per day to lose 1lb per week.

If we assume she needs 2g of protein per pound of bodyweight that means she should eat 140g of protein every day (2 x 70kg).

Since each gram of protein contains 4 calories, that means the protein in her diet accounts for 560 calories (140g x 4 calories). That leaves 1140 calories to come from fat and carbs.

So, how should she split the remaining calories between the two?

OPTION 1

She’s heard that low fat is the way to go and eats 30g of fat. Remember that fat contains 9 calories per gram, so that equates to 270 calories in total (30g x 9).

Add that to the protein intake and we now have a total of 830 calories which leaves a balance of 870 to come from carbs. Carbs have 4 calories per gram so she needs to eat 218g to reach her daily total of 1700 calories.

OPTION 2

She’s heard that low carb is the way to go and eats only 60g, or 240 calories, of carbs. Added to the protein, this accounts for 800 calories. That leaves 900 calories to come from fat which means eating 100g of fat.

So, option 1 looks like:

140g protein = 560 calories
30g fat = 270 calories
218g carbs = 872 calories
Total = 1702 calories

And option 2 looks like:

140g protein = 560 calories
100g fat = 900 calories
60g carbs = 240 calories
Total = 1700 calories

The two examples above should result in the same amount of weight loss as they both equate to the same number of calories.

In reality, one is probably a better option that the other. Which one? I have no idea! The only way to find out would be to experiment and see what works.

Nutrition is very individual and there are all sorts of reasons one might work better than the other for this particular woman. Bear in mind that the other option might work better for her identical twin who also wants to lose weight.

What sort of things would influence the decision?

Here are a few of the more obvious ones…

• what do you enjoy most – fat or carbs?
• what makes you feel fuller for longer – fat or carbs?
• how much activity do you do, and is it competitive? (carbs are a better fuel for optimal performance)
• what effect does it have on your brain function? (carbs are the preferred fuel source for your nervous system)

In future posts, I’ll look at how to work out the number of calories you need in a day; whether or not you have to weigh them all out (I’ll give you a clue…no!); and whether or not all your calories have to come from healthy foods to lose weight (how does the bar-of-chocolate-a-day diet sound?).

Let me know in the comments if you have any questions.