Are Low Carb or Low Fat Diets Better for Weight Loss?

​In the last few years, low carb diets have become more and more popular. But aside from personal preference to have more or less of your diet made up of carbohydrate-based foods - is there any reason to go low carb? 

​This article breaks down some of the ideas around low carb diets and looks at what the science says.

What Are Low Carb Diets?
​

Carbohydrates are one of three primary macronutrients found in food, along with protein and fat. While there is no official definition of a low carb diet, you could consider anything less than 100g carbs per day to be low carb. This is significantly less than most people would consume on a typical Western diet. 

Carbohydrates are found in all vegetables, not just starchy ones like potatoes. They're found in foods that you'd often think of as a side dish, like pasta, rice, or bread. They're in lots of breakfast foods, like cereals, oats, or fruit. And they're in processed sugary treats like candy, desserts, or chocolate. 

"Low carb diet" is a descriptive term, but some low carb diets have specific names. You may have come across the Atkins diet or heard the word "keto". These terms are connected with a lower carbohydrate intake or prioritizing foods in your diet, which have a lower amount of carbohydrates in them. 

What Does Science Say?

There's a lot of research into the question of whether low carb diets are better, more effective, or healthier than any other type of diet. Much of the research has focused on whether low carb diets are better for weight loss than low-fat diets (defined as diets in which less than 30% of the overall caloric intake comes from dietary fats). We've listed three of the many, feel free to check out further studies into the low carb vs low fat debate.

In this research by Brehm, B. J. et al., scientists looked at 53 women who were obese but otherwise in good health and had them follow either a low fat or a low carb diet that lasted 6 months. In the low-fat group, they restricted their calorie intake. The low carb group lost an average of 18.7lb, and the low-fat group lost 8.6lbs - which, after 6 months, was statistically significant. While the low carb group lost 2.2 times more weight than the low-fat group, both groups saw an improvement in their blood lipids (the amount of fat in the blood). Still, there were no other significant differences in their health markers.

Relatedly, Nickols-Richardson, S. M. et al. looked at 28 overweight premenopausal women and put them either on a low carb and high protein or low-fat and high carb diet for 6 weeks. Like the Brehm research above, the low-fat group was also calorie-restricted. The low carb group lost 14.1lbs, and the low-fat group lost 9.3lb - which is statistically significant. They concluded that significantly more weight loss occurred with the low carb diet and - notably, those participants reported less physical hunger than the low-fat dieters.

Compare that with this research by Meckling, K. A. et al looking at 40 overweight people who followed either low fat or low carb diet for 10 weeks. The participants ate the same number of calories. The low carb group lost on average 15.4lb, and the low-fat group lost 14.9lb. That difference was not statistically significant. Although the two groups lost a similar amount of weight, there were improvements in other related health markers.

For example, both groups saw a decrease in blood pressure. Both groups reduced the number of triglycerides. While both groups reduced blood sugar, the low carb group also had a decreased insulin level - showing an improvement in insulin sensitivity. Total cholesterol, specifically the LDL (sometimes thought of as bad) cholesterol, fell in the low-fat group. HDL (sometimes thought of as good) cholesterol rose in the low carb group, but it fell in the low-fat group.

Lastly, research by Christopher D Gardner looked at 609 people either on a low fat or a low carb diet for 12 months! The low fat group lost 11.7 lbs and the low carb group lost 13.2 lbs. Pretty darn close!

Conclusions

The research into low carb diets is conflicting. After controlling for calorie differences, there isn't an overwhelming amount of evidence to support that low carb diets have a more significant impact on the amount of body fat someone can lose than low-fat diets. However, some groups may prefer this way of eating based on personal preference. 

One other key point. These studies above talk about "weight" loss. When you adjust for water weight loss, the fat loss is much closer overall between the two groups.

If you're struggling to lose weight and you're sticking to a calorie deficit over a sustained period, it can be worth asking for a blood test to check for any hormone imbalances. If this is the case, you might want to speak to an RD for guidance on a diet. 

If you feel you need a fitness professional to provide accountability, feel free to reach out for a commitment-free chat about your fitness goals.