If you eat fat you’ll burn fat and if you eat carbs you’ll burn carbs. Science is easy!

So, to start with everyone was on the low carb, ketogenic bandwagon and lost weight. Now it appears that low fat is making a comeback because low fat makes you lose weight too. Confused? Me too! Why do they both work and which is the best structure to follow if you actually want some form of sustainable weight loss?

Low Carb was the initial hype because carbohydrate is the preferred source of energy for the body, so if the body has carbs it will use them as fuel first. Carbohydrate is far easier for the body to utilise as it requires less oxidation however it consequently yields less energy than a molecule of fat. So if we don’t have any carbohydrate floating around and available for use it makes sense that our body will then begin to tap in to our fat stores. At high intensities it becomes a lot more difficult to use fat as we can’t get enough oxygen to the molecules to fully oxidise it so that the free fatty acids can be released and enter the metabolic pathways that produce energy. This makes it significantly more difficult to train at high intensities on a ketogenic diet.

Many people swear by low carb as they’ve seen some pretty remarkable weight loss. The reason people miraculously lose weight is nothing more than energy deficit. By getting rid of the carbohydrate you cut out a proportion of your energy intake. Less calories in and more calories out = weight loss…. Magic. Even though people swear that they’re eating more on their low carb diet they tend to replace their carbohydrate heavy foods with less energy dense foods such as vegetables and legumes.

Another factor often overlooked is water retention. Carbohydrate stores 3.5 units of water per unit of carb. That’s a lot of water! Reduce your carbs and you reduce the ability of your body to hold water.

Then we come to low fat and the confusion begins all over again. From advocating a high fat, low carbohydrate diet for weight loss many fitness gurus and media outlets are now suggesting that we turn our attention back to low fat.

Time for a revelation. By going low fat you essentially do the same thing to your body as you do by following a ketogenic diet; you move in to a calorie deficit and then lose weight. As fat is worth 9kcal per gram compared to the 4kcal contributed by protein and carbohydrate, is it really any wonder that low fat aids weight loss?

The low fat trend resurfaced recently after a surge in media articles relating to research published comparing the effects of low carb vs low fat for fat loss. This research showed that dietary fat restriction led to greater levels of fat loss in obese individuals over a two week period. Other research, such as a meta-analysis conducted by the National Institutes of Health and American Diabetes Association, has shown that there is no weight loss intervention strategy that more preferable.

So where does this leave us?

When it comes to weight loss and body fat loss what’s best? It all comes down to what is more sustainable in the long term. If you are able to maintain a low carbohydrate diet (although goodness know why anybody would want to do that!) then go for it. If low fat is easier for you then brilliant, a low fat diet may well be the answer. Personally I believe that a healthy balance is always preferable to an exclusion diet and will allow you to consume the full spectrum of nutrients that are needed by the body for a healthy, happy and balanced existence.


- Charlotte Fisher


Nutritional Science Student