Brain fog is a real part of dieting for many people, especially those who choose to start a very low carb diet. Low carb diets have many benefits but switching from a diet heavier in carbohydrates to a keto or low carb regimen can be difficult in the beginning! It’s called the keto flu for good reason, as the body switches from using glucose as fuel to ketones, bringing with it all kinds of malaise. Even if you aren’t cutting out carbs entirely, sluggishness and brain fog can make it seem impossible.
It’s important to remember these effects are temporary, and to remind yourself of all the reasons why you’re making a switch. It could also be helpful to remind those around you that it’s not just all in your head: a study found that reducing carbohydrates directly affects your cognitive skills.
From 2008, Tufts University followed healthy adult women who chose to eat a low carb diet or a low-calorie diet that was balanced with macronutrients. It was a small study of only 19 women, but the research team believes they found evidence that reducing carbohydrates resulted in poorer cognitive performance than reducing overall calories.
Participants took cognitive tests that measured attention, visual attention, and memory (long-term, short-term, and spatial) before their new diets started, during the first week, and after carbohydrates had been added back in for those on the low carb plan.
The dieters on the low carb plan experienced a steady decline in memory, their reaction time became slower, and visual and spatial memory performance was lower than those in the low-calorie group. A silver lining was found, however—the low carb dieters paid better attention, something researchers believe is due to the higher protein and higher fat content of the low carb diet which is known to improve short term memory.
Did the participants notice any difference when carbs were restricted versus when calories were restricted? Surprisingly, no difference in hunger was noted between the two, but the low-calorie group reported confusion at the study’s midpoint.
Clearly, there are trade offs when choosing one diet plan over the other! When on a low-carb diet that restricts glucose sources (carbs), poorer cognitive performance prevailed, likely due to the fact that the brain utilizes glucose for energy directly. Lower levels of glucose impact the brain’s functioning and energy reserves. Low-carb diets should not be confused with keto diets when the brain and body are primed to start using ketones as fuel, rather than glucose.
For those skipping their morning bagel in favor of a high protein omelet, understanding that your brain is running a little behind could help you persevere—or at least help you accept that you’ll need to set extra reminders and take your time while driving!
Danci et al. Low-carbohydrate weight-loss diets. Effects on cognition and mood. Appetite, 2009; 52 (1): 96 DOI: 10.1016/j.appet.2008.08.009