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Dairy at Breakfast Provides a Cognitive Boost

    Tasty homemade granola with yogurt and berries on grey table, closeup. Healthy breakfast.

    Written by: Lauren Milligan Newmark, Ph.D. | Issue # 119 | 2024

    • One of the many proposed health benefits of eating breakfast is short-term improvement in cognitive performance.
    • Two experimental studies found improvements in blood glucose levels, amino acid availability, feelings of fullness, and concentration when subjects consumed a dairy protein-rich breakfast compared with a carbohydrate-rich breakfast or skipping breakfast.
    • Dairy foods, including milk, cheese, and yogurt, have a low glycemic index and high protein content, which may be beneficial to cognitive functioning. 

    For every faithful breakfast eater, there is an equally devoted breakfast skipper unwilling to concede that it is the most important meal of the day. The science on the benefits of breakfast-eating is just as divided as the general public’s opinion. Although some studies have found regular breakfast eaters have a higher IQ or improved cognitive performance compared with those who frequently skipped the meal [1-6], other studies [7-9] found no relationship between breakfast-eating and cognitive capabilities. 

    One potential reason for these conflicting results is that most studies have been observational and considered only whether study subjects ate breakfast rather than what they ate for breakfast. From toast with jam, to eggs and ham, breakfast foods vary widely in nutrients that influence satiety (i.e., feeling full) and blood glucose levels, factors that are associated with cognitive performance [10]. When it comes to boosting brain power, not all breakfast foods are created equal—but which are optimal? Two new experimental studies [11, 12] highlight the important role of dairy in increasing satiety, regulating blood glucose levels, and improving cognitive concentration. 

    Just like our muscles need fuel for a workout, the brain requires energy—specifically, glucose—for memory and concentration. After an overnight fast, the body’s glucose stores are depleted. Breakfast replenishes the body’s glucose stores. Previous research [reviewed in 13, 14] suggests foods that have a low glycemic index provide the greatest benefit to cognitive performance. These  foods result in a lower blood glucose peak and stable levels of blood glucose over a longer period. 

    Carbohydrate-laden foods, like muffins, bagels, and donuts, provide plenty of glucose but do so in a quick spike followed by a drop in blood sugar levels—thus, they have a high glycemic index. Dairy foods, such as milk and yogurt, do contain carbohydrates but they have a low glycemic index because their carbohydrates are digested alongside milk proteins. 

    Whey proteins contain amino acids that have an insulin-stimulating effect that keeps blood sugar levels stable after a meal. In fact, these insulin-stimulating effects might even help limit glucose spikes from other sugar-filled foods consumed along with dairy [15]. Milk’s other protein class, casein proteins, plays an important role in maintaining a steady level of blood glucose. Whereas whey proteins are quickly broken down by digestive enzymes, caseins form an insoluble curd in the digestive tract, which slows digestion. In addition to promoting satiety, which can also impact concentration [10, 11, 13], slow casein digestion stimulates the production of gastric hormones that also can slow down the digestion (and therefore the transfer into the blood stream) of milk sugars [16]. 

    Dairy’s slow-digesting and insulin-stimulating proteins were tested against a carbohydrate-rich breakfast or no breakfast at all in two experimental studies [11, 12]. Both studies used a clever experimental approach called a crossover design. Rather than give one group of study subjects test meal A, another test meal B, and then compare the effects of meals A and B between subjects, crossover studies give each study subject meal A and meal B (or no meal at all) in random order and compare the effects of these meals within subjects. In doing so, crossover studies eliminate variability between subjects, such as in level of education, body mass, age, or daily caloric intake that can potentially influence metrics of interest like blood glucose levels or performance on a cognitive test. However, these studies are usually done over a short period of time, as human subjects could potentially gain weight and change their diet and lifestyle over months or years, and most definitely age over time. 

    In the first study [12], 20 healthy Dutch men and women between 20 – 40 years of age consumed three different test meals in random order. Test meals were consumed on the same day of the week and separated by either seven or 14 days as a “washout” period. The night before the test breakfast, all study subjects consumed the same standardized meal at 7:00pm. 

    The researchers tried to select test breakfasts like what a typical Dutch person might consume for breakfast, making sure that each meal was identical in total calories and total fat. Meal one was three slices of white bread, with a set amount of margarine (to stay dairy-free) and strawberry jam, along with black tea with sugar; meal two was identical to meal one except 250 ml of semi-skimmed cow milk replaced the black tea; meal three was three slices of white bread, 250 ml semi-skimmed cow milk, and 35 grams of low-fat Gouda cheese (this is The Netherlands, after all). 

    Results from blood samples taken at several intervals in the five hours after the test meal suggested that replacing carbohydrates (meal one) with one serving of dairy protein (meal two) increased the availability of amino acids and reduced the blood glucose response. Results also suggested that replacing carbohydrates with two servings of dairy (meal three) had these same effects plus increased satiety and an increase in the plasma concentration of glucagon-like peptide 1 (GLP-1), a hormone that promotes insulin secretion [12]. The increase in GLP-1 was believed to result from  an increase in both dairy protein and in calcium, suggesting that replacement with other protein types may not have the same physiological response. Unfortunately, this study did not measure cognitive performance, which has previously been linked to sustained glucose levels and increased plasma concentrations of amino acids, especially branched-chain amino acids like leucine that are found in high levels in dairy products [11].

    The second study [11] was conducted on 30 Danish women between the ages of 18 and 30 years old with a BMI >25 kg/m2 (the current metric used to identify someone as overweight or obese). The three test breakfast meals (again, assigned in random order) were a high-protein, low-carbohydrate meal (300 grams of high protein yogurt and 30 grams of oats), a low-protein, high carbohydrate meal (60 grams of whole grain bread with 30 grams of raspberry jam and 250 grams of apple juice), or no meal (only water). The meals (except for water) were matched for calories, fat, dietary fiber, and weight. Like the Dutch study, meals were selected for their familiarity with subjects. All meals were consumed at the study center after a 12-hr fast and participants had at least one day off in between each test meal for washout. Blood samples were collected before consuming the test meal, and then at regular intervals until 170 min after meal completion. Concentration (as a measure of cognition) was determined 150 min after meal completion using the paced auditory serial addition task (PASAT), which was probably about as fun to take as it sounds; 61 single-digit numbers were announced from an audio file every three seconds and participants added  the number to the previous one, saying the ongoing sum out loud [11].

    Subjects reported feeling more satiated and less hungry after consuming the dairy-protein rich breakfast compared with the carbohydrate-rich breakfast and no breakfast at all, despite no significant differences within-subjects across the three test meals in plasma levels of appetite-regulating hormones such as ghrelin [11]. Compared to their scores from the day without breakfast, participant PASAT scores improved on the high-protein test meal day but not the high-carbohydrate day. Although these results were not statistically significant, a 3.5% difference in scores from the same test taken at most two weeks apart seems noteworthy (keeping in mind the order of meals was random, and some participants had their high-protein meal first whereas others had it last—so you can’t account for “learning”). It would be worthwhile to repeat this type of study in a more heterogenous study population (both men and women, various body weights, various ethnic backgrounds) so the results could be extrapolated more widely. 

    Regardless, it is remarkable that in both the Dutch and Danish studies the researchers found within subject differences despite the subjects only consuming each test meal on one occasion and completing the study within the span of days and weeks, rather than months or years. It is estimated that nearly 25% of Americans regularly skip breakfast [17]. Some may skip because of lack of time, others for lack of hunger—but the results of these studies suggest that even eating breakfast with dairy foods like milk, yogurt or cheese on occasion could influence their health and mental acuity. And that goes for the other 75% of us that regularly eat breakfast, too. 

    References

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