Ohio State research team conducted a double-blind, randomized crossover trial to determine if the type of dietary fat could impact cognitive function. The subjects were 51 women (n = 32 breast cancer survivors, n = 19 noncancer controls; mean ± SD age: 53 ± 8 y). The researchers assessed the cognitive function of their subjects by having them complete a baseline assessment of their attention during a morning visit to the research lab. The tool used, called a continuous performance test (CPT), is a measure of sustained attention, concentration, and reaction time based on 10 minutes of computer-based activities.

Annelise Madison works in the lab of Janice Kiecolt-Glaser, a professor of psychiatry and psychology and director of the Institute for Behavioral Medicine Research at Ohio State. For this work, Madison conducted a secondary analysis of data from Dr. Kiecolt-Glaser's prior study assessing whether high-fat meals increased fatigue and inflammation among cancer survivors.

All subjects had their blood drawn to assess endotoxemia markers LPS binding protein (LBP), soluble CD14 (sCD14), and the LBP to sCD14 ratio one hour prior to eating either a large (930kacl) meal that was either high in saturated or monounsaturated fatty acids. The same meal was prepared with either palm oil or oleic acid sunflower-oil meal. The women again completed the CPT 5 hours after completing each meal on two different days separated by a week or more. Both meals were the same nutritionally except the meal made with palm oil was high in saturated fat and the other meal made with sunflower oil was high in unsaturated fat. Their performance on a CPT was significantly worse 5 hours after eating the palm oil-rich meal than after they consumed the same meal containing sunflower oil. [1]

These Ohio State researchers were looking at whether a condition called “leaky gut”, which is claimed to allow intestinal bacteria or parts of those bacteria to enter the bloodstream. This is claimed to lead to more endotoxins in the blood that are believed to increase inflammation and perhaps in other ways may adversely affect one’s ability to concentrate or to focus one’s attention on a task. However, the “leaky gut syndrome” is a dubious speculative hypothesis at best. The authors of this study suggest endotoxins from the gut may enter the blood and then pass into the brain “leaky brain syndrome” and interfere with brain function. This speculative explanation of their findings is at best dubious according to Science-Based Medicine authors. If leaky guts and brains are pseudo-sciences, then what might explain their findings?

A More Science-Based Mechanism is Needed

It is known that large meals high in fat can markedly increase postprandial lipemia and may trigger inflammation and endothelial dysfunction. This might impair blood flow to the brain for a few hours after a large high-fat meal compared to a meal low on fat and high in cereal fiber.[2] Could it be a transient reduction in blood flow to the brain that may be a more viable hypothesis to explain why a large, high-fat meal may be negatively impacting the ability of these women to focus their attention?The high-fat meal used in this study contained eggs, biscuits, turkey sausage, and gravy, and 60 grams of fat, either a palmitic acid-based oil high in saturated fat or the lower-saturated-fat sunflower oil. Both meals totaled 930 calories and were 58% fat calories.

The researchers stated the meals were designed to mimic the contents of various fast-food meals such as a Burger King double whopper with cheese or a McDonald's Big Mac and medium fries. Serum triglyceride levels typically peak in the blood about 4 to 5 hours after such a large high-fat meal used in the Ohio State study.

According to Annelise Madison, lead author of the study and a graduate student in clinical psychology at The Ohio State University: "Because both meals were high-fat and potentially problematic, the high-saturated-fat meal's cognitive effect could be even greater if it were compared to a lower-fat meal." Perhaps, but why would the saturated fat-rich meal promote more inflammation and impair cognitive function? Five hours after the meal the women subjects took the continuous performance test again. Between one and four weeks later, they repeated these steps, eating the opposite meal of what they had eaten on the first visit.

Researchers also analyzed participants' fasting baseline blood samples to determine whether they contained an inflammatory molecule that signals the presence of endotoxemia—the toxin that escapes from the intestines and enters the bloodstream when the gut barrier is compromised.

After eating the meal high in saturated fat, the subjects were, on average, 11 percent less able to detect target stimuli in the attention assessment. "If the women had high levels of endotoxemia, it also wiped out the between-meal differences. They were performing poorly, no matter what type of fat they ate," Madison said. Now, the study did not determine what was going on in the brain. Madison said previous research has suggested that food high in saturated fat can drive up inflammation throughout the body, and possibly the brain. Fatty acids also can cross the blood-brain barrier. This might explain why the saturated fat-rich meal impaired the ability of their subjects to focus even more than the same meal with far more unsaturated fat.[3]

Bottom Line:

While the suggestion that leaky gut syndrome plays a role in this study’s results seems dubious the author’s data does suggest that a large high fat meal and particularly one high in saturated fat may impair one’s ability to focus for several hours after such a meal is not all that surprising. After all, how many people struggle to pay attention after a large Thanksgiving Day meal? This reviewer would suggest the authors of this study refocus their attention on a more viable mechanism to explain their results than the very dubious notions of “leaky guts” and “leaky brains”.

By James Kenney, Ph.D., FACND

References:

[1] Madison AA, Belury MA, Andridge, et. al. Afternoon distraction: a high-saturated-fat meal and endotoxemia impact post-meal attention in a randomized crossover trial, Am. J. Clin. Nutr. May 2020 or https://academic.oup.com/ajcn/advance-article-abstract/doi/10.1093/ajcn/nqaa085/5835679?redirectedFrom=fulltext].

[2] Brock DW, Davis CK, Irving BA, et. al. A high-carbohydrate, high-fiber meal improves endothelial function in adults with metabolic syndrome. Diabetes Care 2006;29:2313-15. or https://care.diabetesjournals.org/content/29/10/2313

[3] Margorious AM. Fatty acids and postprandial inflammation. Curr Opin Clin Nutr Metab Care. 2009;12:129-37 or https://www.ncbi.nlm.nih.gov/pubmed/19202384