Why carb crashing is not the secret to weight loss

This article isn't meant to dismiss low carbohydrate diets for weight loss. Low carb diets can work but it is the reduction in total calories and eating below your maintenance calories which results in the loss of weight and body fat, not just a reduction in carbohydrates. A low-carb diet might also be better for some people for both fat loss and maintaining a healthy weight because it helps them adhere to a healthier way of eating (i.e. – making better food choices) and the increased fat and/or protein intake might increase satiety levels and prevent them overeating. Low-carb diets might also make some people feel more energetic and spritely, making their workouts more fun and something they look forward to. In contrast though, other people might feel utterly terrible: unable to concentrate (foggy head), no energy to perform adequately in the gym, make poor food choices, crave carbohydrates and be unable to adhere to their plan.

So, if it's not the diet we want to address then what is it? It is the idea that “carbs will make you fat” and the carb-phobia that some people now have. It is the number of calories you consume versus the amount of energy you expend over a prolonged period which will make you either gain or lose weight.

We also want to explain a process which all our bodies perform: de novo lipogenesis (DNL). This is the metabolic process by which our bodies convert excess carbohydrates into fatty acids which are then incorporated into triglycerides for energy storage in both the liver and adipose tissue (subcutaneous fat). So yes, carbs can be converted into and stored as fat in our bodies however the rate at which this occurs is much lower and less significant than people who see carbs as the enemy would have you believe. 

Numerous studies in which participants were over-fed and given excess carbohydrates show that DNL only makes a small contribution to any increase in total fat stores and does not account for the entire increase in body fat.

So, if the excess carbs are not turned into fat then does this mean one can eat unlimited amounts of carbohydrates? No, during overfeeding of carbs there is increased carbohydrate oxidation and a reduction in fat oxidation (or fat used for energy) resulting in a positive fat balance and an increase in the net storage of the fat consumed from one's diet.

Alternatively, an over-feed of fat will also increase fat storage. While one will burn more fat, the fact that there is more fat being consumed and total calories are still in excess means that the net fat balance is still positive and dietary fat will be stored. So unfortunately, regardless of whether the excess calories you consume come from the carbohydrates or fats, the fat balance in the body will be positive and you will gain body fat.

For both carbs and fat, the excess calories and resulting positive fat balance need to be present for a prolonged period to lead to significant increases in body fat. A single high-carb or high-fat meal or day might initially result in a transient positive fat balance and the storage of some dietary fat as body fat, but this will be balanced out throughout the rest of the day or coming days providing there isn't a prolonged excess of total calories.

Are low-fat diets better?

Are low-fat diets better than low carb diets for maintaining a healthy weight and not putting on excess body fat? No, again it is not so straightforward. If we overeat but consumed very little fat and mostly carbs, we might potentially get less body fat than if we ate a greater proportion of dietary fat. However, this is unrealistic as fats are important for other processes and are not just used for energy. We need them to produce hormones, cellular membranes, and for nutrient uptake. Although DNL increases when dietary fat is extremely low it might not necessarily be able to provide all the fat our bodies need. This is especially true in terms of the essential fatty acids that our bodies cannot produce and must be consumed through our diet. A prolonged extremely low-fat diet would lead to an unhealthy physiology and eventually death.

Now some might be asking: what about protein? The short answer is that an excess of total calories from protein will behave in a comparable manner to carbohydrates. Protein oxidation will increase while fat oxidation decreases leading to a positive fat balance and net storage of fat.

What do all successful weight loss diets have in common?

They all create an energy deficit over a prolonged period of time leading to a negative fat balance and a reduction in total body fat. As mentioned earlier, there isn't a single successful way of decreasing caloric intake and different approaches will work for different people. You don't need to be extreme or completely avoid consuming one of the macronutrients. Each macro has a unique effect on the body so altering the ratios will be beneficial for different people.

Other strategies such as increased fat intake or consumption of soluble fiber can help slow digestion and increase satiety, helping people eat less overall. Some people will need a more carbohydrate-rich diet to fuel their workouts while others, especially if they are obese, might benefit initially from consuming less.

There isn't a single way to diet but, evidence-based  dietary recommendations that are healthy and sustainable for the long term and we won't endorse extreme diets of any variety.