In recent years, scientists have studied the effects of low fat versus low carbohydrate diets on cognition and mood. In one study, women who followed a carb free diet for a week showed impaired memory compared to those who adhere to a more balanced, reduced calorie plan. When the low-carb dieters added small amounts of carbohydrates to their regimen the following week, it reversed the cognitive impairment. In another study, lasting a year, low-carb and low-fat dieters did equally well in memory and cognition tests, but people in the low-fat group scored higher on measures of mood. Experts say that cutting carbs might impair cognition by reducing the blood level of glucose, which is produced when carbohydrates are broken down during digestion and which serves as the brains primary fuel source.
If you’re considering a low-carb diet, look for one that allows some complex carbohydrates in the form of fruits, vegetables, and whole grain. That might help mitigate crankiness or brain fog.