If you love a low carb diet, this article will put your bias to the test. Evidence-based nutrition is not about picking a tribe and defending dogmatic rhetoric. You need to be teachable and open to new research as it becomes available. Of course, one study won’t always cause a seismic shift in scientific opinion. But it may add to the debate and alter out thinking somewhat.

The Low Carb Diet Vs The Low Fat Diet: Study Background

This article relates to a 2020 study by Hall et al. The study compared a low-fat vegan diet vs a low-carb Keto diet. Already low carb diet stalwarts might be getting nervous. And once you see the results, a few people might be sore in the nutritional butthole. Because the study challenges long-standing views and rhetoric yet again. So the question is, are you open to new evidence or are you already on the defensive before we even get started?

Before we look at the detail of the study, it’s worth noting one thing. The research wasn’t designed to tell you which diet is best for fat loss. It was not a weight-loss study. Researchers shielded participants from weight measurements, so as not to influence their behaviour. They even forced them to wear loose-fitting clothes during the study. The study is also not claiming that a vegan diet is better than an omnivorous one, or vice versa. So don’t interpret the findings in this way. To do so would be a little gimpish—new word, claiming it.

Researchers controlled all food intake of the participants, which is significant. There was no room for miscalculation of calories. No misreporting of intake or hiding the 5 doughnuts someone had for lunch. The degree of control gives the study a high degree of reliability. A good start, you might say.

Participants were split into 2 groups, 10 in each group. Group 1 had a macro breakdown of 75% Fat, 15% Protein, and 10% Carbs. The second group ate 75% Carbs, 15% Protein, and 10% fat–this group was the vegan group.

For 2 weeks participants ate 3 meals a day (+ snacks) with the prescribed macro breakdown. The food made available was twice their estimated maintenance calories. Subjects could eat as much or as little as they wanted until they reached the point of fullness. Then, after 2 weeks, subjects switched to the alternative diet. So, if the Keto advocates are right, the study should show that those on the low carb diet should eat less. But what did the study show?

The Results

Well, the study didn’t back up the low carb diet theory. In fact, those following the low-fat diet consumed on average 689 kcals less per day, compared to the high-fat group. And that’s a huge difference. Especially if you’re trying to manage your nutrition and control calories.

The low carb diet group did burn around 166 kcals more per day, which offset some of the extra food intake. But not enough to balance the elevated intake. And, to a degree, you would expect elevated activity levels with so many extra calories.

One thing that Keto stalwarts will jump on straight away is the length of the study.

“If they were only on the diet for 2 weeks, then they wouldn’t have been in ketosis. The study needs to be much longer to be a fair reflection of reality.”

Hmmm. Nice theory, but it doesn’t seem to play out that way in the study. In week 2, participants achieved maximal levels of ketones in the bloodstream. So what did this do for appetite and calorie intake? A bit, but not much. Hunger did decrease in week 2 for the low carb diet group, yet they still consumed c.544 kcals more per day. Again, not an insignificant amount of calories.

Although this wasn’t a weight-loss study, it highlighted show some interesting outcomes. Those on the low carb diet lost 1.8kg over the course of the 2 weeks. “That’s great!” you might think. But here’s the kicker. 1.6kg of that wasn’t fat. It was weight loss related to glycogen, water fluctuations, and other variables. In comparison, the low-fat group lost 1kg of body fat. So a great reminder that focusing on scale weight is deceiving. I mean, what would you prefer? To see 1.8kg reduction on the scale, but only 0.2kg of it to be from fat, or a 1kg reduction, with less than 0.2kg coming from FFM? I know which one I’ll be aiming for.

So if this study wasn’t designed to tell you which diet is best for fat loss, what is it saying?

The Low Carb Diet: Study Outcomes And Takeaways

Here are the highlights and take-home messages from the study.