Skip to main content
food for thought

Oily fish such as salmon is high in Omega-3 fatty acid and has anti-inflammatory effects on the brain, keeping cell membranes flexible so memory messages can easily pass between them.iStockPhoto / Getty Images

If your productivity wanes in the afternoon, consider what you eat for lunch.

According to researchers from Ohio State University, eating just one meal high in saturated fat can hinder your ability to concentrate. And if you have a “leaky gut,” eating any type of fatty meal could impair your thinking skills.

While previous research has linked a long-term, high-fat diet to impaired cognitive function, this new study found that eating a single high-saturated-fat meal also has cognitive consequences.

About the study

The study, published online this month in The American Journal of Clinical Nutrition, compared how 51 women, with an average age of 53, performed on an attention test after they ate a meal high in saturated fat or unsaturated fat.

Saturated fats are found in animal foods such as meats and fatty dairy products, as well as some plant oils, including coconut oil and palm oil. Unsaturated fats come from vegetables, seeds, nuts, olives and fish.

At the outset of the study, all women completed a “continuous performance test,” a tool that measures sustained attention, concentration and reaction time based on 10 minutes of computer activities.

Participants then ate a fatty meal designed to match the fat and calorie content of a fast-food meal (for example, a cheeseburger and fries). The two test meals each contained 60 grams of fat, one from palm oil (saturated) and the other from sunflower oil (unsaturated).

Five hours after eating a test meal, the women took the attention test again. A few weeks later, each participant completed the same protocol but ate the other high-fat meal.

After eating the high-saturated-fat meal, women had more difficulty performing the attention test than they did following the meal high in unsaturated fat.

The researchers also found that women who had leaky gut, or intestinal permeability, scored worse on the attention test no matter which high-fat meal they had eaten. Leaky gut was identified by elevated blood levels of bacterial endotoxins (a substance found in the cell wall of bacteria).

Leaky gut occurs when the lining of the gut becomes more permeable than normal, allowing bacterial endotoxins to pass into the bloodstream, which can cause inflammation. Genetics, poor diet, heavy alcohol use and stress may increase intestinal permeability.

When consumed in excess, saturated fatty acids can cross the blood-brain barrier and interact with brain cells, triggering an inflammatory response that could impair concentration. Bacterial endotoxins that escape from a leaky gut into the bloodstream may also interfere with cognition.

What are the caveats of the study?

The study was conducted in women; it’s not known if the same results would occur in men. The researchers also didn’t assess how long attention was impaired after eating the high-fat meal.

As well, the participants’ oral health was not considered. While intestinal permeability is the main source of bacterial endotoxins, poor oral health can also contribute.

What are the best foods for cognitive health?

Your diet can affect mental effectiveness by supplying nutrients and phytochemicals necessary for brain function.

1. Omega-3′s and choline
  • Omega-3’s. DHA (docosahexaenoic acid), found in oily fish such as salmon, trout and sardines, is the dominant omega-3 fatty acid found in the brain. There, it has anti-inflammatory effects and keeps brain cell membranes flexible so memory messages can easily pass between them.
  • Choline. A higher intake of this B vitamin-like compound has been tied to improved memory performance in healthy adults. It’s needed to produce acetylcholine, a key brain chemical for mental focus and learning.
  • What are good sources of Omega-3′s and choline? include egg yolks, soybeans, beef, chicken, cod, red potatoes, shiitake mushrooms, kidney beans, quinoa and yogurt.
2. Vitamin E
  • Vitamin E. As an antioxidant, vitamin E plays a key role in protecting brain cells from free-radical damage. High blood levels of vitamin E have repeatedly been associated with better cognitive performance.
  • What are good sources of Vitamin E? Almonds, hazelnuts, wheat germ oil, frozen spinach, sunflower oil, safflower oil, grapeseed oil and peanut butter are excellent sources.
3. Flavonoids
  • Flavonoids. Growing evidence suggests that these phytochemicals may benefit cognitive function by suppressing inflammation and fending off free-radical damage in the brain.
  • What are good sources of flavonoids? Flavonoid-rich foods include berries, red grapes, red cabbage, pears, green tea, cocoa, onions, kale, broccoli, citrus fruit, parsley, celery and soybeans.
4. Monounsaturated fat
  • Monounsaturated fat. This unsaturated fat helps reduce inflammation in the body; consuming mainly monounsaturated fat versus saturated fat has been associated with better cognitive scores among women.
  • What are good sources of monounsaturated fat? Good sources include olive oil, olives, avocado, peanuts, peanut oil, almonds, cashews, pecans and pistachios.

Leslie Beck, a Toronto-based private practice dietitian, is director of food and nutrition at Medcan.

Sign up for the weekly Health & Wellness newsletter for the latest news and advice.