Low Carb Diet: Is It The Only Way To Lose Weight?

“Avoid Carbs.” “Don’t eat sugar.” “Stay away from bread.” When asking for diet advice, you may hear one or more of these sayings. But why? Where did low carb craze come from? Is it the best way to lose weight?

In this article I will answer the following questions: Where did the low carb pandemonium come from? Is low carb effective? Is it the only way to diet? I want to state that this article is not a low carb bash. If you like low carb, great! If you lost weight on low carb, even better! That still doesn’t mean it’s for everyone.

First things first, where did the idea of low carb come from? The biggest supporter of the low carb diet is the carbohydrate-insulin model (CIM). It is known that carbohydrate increase blood glucose levels, initiating the release of insulin. The CIM states that high levels of insulin shuts down the release of fatty acids (fat oxidation) to be used by the body and shuttles the circulating fat into adipose tissue and away from the tissue that needs it. This decrease in fuel availability in the blood cause the body to enter a “starvation mode” on the cellular level. Furthermore, decreasing energy expenditure and increasing hunger. This later portion of the model leads to the hypothesis that someone could store calories even if consuming relatively low calories.

Makes sense, right? Most models do. The only problem is this model did not hold up well when tested.

"The biggest supporter of the low carb diet is the carbohydrate-insulin model (CIM)"

---

In a 2015 study(1), Dr. Hall set out to test the CIM. This study had 19 adults in a metabolic ward for 2 weeks (the gold standard of tracking weight loss and energy expenditure). They put participants through either a 6 day low fat or low carb diet. After a washout period, they switched diets. Both diets were isocaloric (same amount of calories) and had the same percentage of calories from protein (about 20%).

So what did they find? Is the CIM valid? Did they lose weight? Did they prove that carbs make us fat?

After 6 days of a low carb diet (30% of calories from carbs) the participants increased their fat oxidation and lost weight just like the model predicted! BUT after 6 days of low fat diet (70% of calories from carbs) there was relatively no change in fat oxidation and participants lost MORE fat than the low carb diet! The fat loss difference was small but it showed that decreasing carbs and increasing fat oxidation was not the only way to achieve fat loss like the CIM predicted.

---

Like I said, this isn’t an article to bash low carb. Low carb diet was effective at losing weight. In fact, there is a great deal of research showing low carb diets does induced fat loss. That being said, the biggest take away is that low carb is not any more effective than low fat.

You may be thinking, if it is not any more effective than any other diet why have so many people had success with the diet?

The main reason people have success on a low carb diet is because they decrease their calories! Cutting out or lowering a single macronutrient, whether it is fat or carbs, is an effective way to decrease your total calories consumed. A calorie deficit is the driving force behind any weight loss.

Most individuals can pick out things that are higher in carbs: rice, bread, pasta, grains. Even more, people tend to cut out the junk food or the food that makes it so much easier to over consume calories. The ability to identify foods to avoid and being more conscious of food intake is paramount in an individual’s attempts to lose weight.

"That being said, the biggest take away is that low carb is not any more effective than low fat"

---

But that was one study, they only “dieted” for 6 days. Can we draw conclusions based off this? If this was the only study that showed no difference then no, we couldn’t draw conclusions but there are massive amounts of studies out there that compare multiple studies and draw the same conclusion. (2,3)

A review article done in 2019 looking at all the low carb vs low fat research concluded with “..at this time, the current evidences do not strongly favor low carbohydrate or low-fat diets for weight management”(4). It is the general consensus, in the scientific field, that low fat or low carb have no difference in weight loss.

To bring it all together, low carb is an effective way to lose weight. It gives people with a way decrease calories, but it is not the only way to lose weight. Weight loss is driven by a calorie deficit. Whether you go low carb or low fat, the most important factor in losing weight is your ability to sustain a calorie deficit.

References:

1. Hall KD, Bemis T, Brychta R, Chen KY, Courville A, Crayner EJ et al. Calorie for calorie, dietary fat restriction results in more body fat loss than carbohydrate restriction in people with obesity. Cell Metab 2015; 22: 427–436.

2. Hall, K. D., & Guo, J. (2017). Obesity energetics: body weight regulation and the effects of diet composition. Gastroenterology, 152(7), 1718-1727.

3. Johnston, B. C., Kanters, S., Bandayrel, K., Wu, P., Naji, F., Siemieniuk, R. A., ... & Jansen, J. P. (2014). Comparison of weight loss among named diet programs in overweight and obese adults: a meta-analysis. Jama, 312(9), 923-933.

4. Seid, H., & Rosenbaum, M. (2019). Low Carbohydrate and Low-Fat Diets: What We Don't Know and Why we Should Know It. Nutrients, 11(11), 2749.