By: Carly Gruneberg
Nutrition Guidance Provided By: Kaylyn Koons, MS, RD, LDN
Carbohydrates: The misunderstood macronutrient
Throughout history, carbohydrates have been villainized in the public eye. Claims of carbohydrates causing weight gain and chronic disease have convinced many people to eliminate them almost entirely from their diets. In reality, our brain is fueled by carbohydrates, and inadequate consumption of them prevents our brain from functioning as efficiently as it can.
When you cut carbs too low, your body doesn’t have enough glucose (its preferred energy source) to function normally. To compensate, it shifts into a state called ketosis, where it starts using ketones made from fat for energy instead. While this keeps you alive, it’s not the body’s first choice, and the switch is why many people experience symptoms like fatigue, constipation, and dizziness when starting very low-carb diets like keto (Shalabi et al., 2021).
This becomes even more worrisome when we consider that nearly 25% of our daily energy expenditure is spent on brain function alone (Chen & Zhang, 2021). This means that our ability to think and learn at our highest potential is closely tied to the foods we choose to eat. Our brain operates best when we give it a steady supply of glucose from complex carbohydrates and whole foods. These would include whole grains (oats, brown rice, whole grain pastas & breads), legumes (chickpeas, beans & lentils), starchy vegetables (sweet potatoes are great!), and whole fruits.
Fiber: The forgotten hero of nutrition
Another risk of eating a low-carbohydrate diet is its inherent lack of dietary fiber. Fiber is a type of carbohydrate that the human body cannot digest due to the absence of the necessary enzymes. Although humans are not able to draw energy from dietary fiber, its impact on our health is significant. It slows digestion and the absorption of glucose into the bloodstream after a meal by adding bulk to the digestive tract. Without regular fiber intake, your blood sugar will spike, prompting the body to compensate by increasing insulin release to facilitate glucose uptake into cells (Muth & Park, 2021). Over time, large influxes of insulin in response to overconsumption of simple carbohydrates can lead to insulin resistance. This is when your body cells stop responding to insulin signals effectively and our cells are not able to properly uptake its fuel source, glucose. You may recognize this as being the primary mechanism of Type 2 Diabetes, but it can also contribute to a range of other health problems on its own.
Conversely, diets high in fiber support glucoregulatory processes, resulting in more stable blood glucose levels. This stability is associated with better cognitive performance, particularly memory, as we age (Muth & Park, 2021). It may also increase the chances of beneficial aging outcomes, defined as the “absence of disability, depressive symptoms, cognitive impairment, and chronic disease” (Muth & Park, 2021). Despite its essential role in health, fiber is often overlooked, especially in mainstream media, where protein tends to dominate the spotlight.
What’s the deal with added sugars?
In contrast to fiber-rich complex carbohydrates that promote stable blood glucose levels, simple sugars create rapid spikes and crashes, which may negatively impact attention, memory, and overall cognitive performance (Muth & Park, 2021). Excess added sugar intake can also increase inflammation and oxidative stress, both of which are known to damage neurons, essential units of the brain & nervous system, and impair cognitive function over time (Muth & Park, 2021).
“Simple” carbohydrates are not just the sugar and syrups found in candy, soda, and sweets. White flour, and thus white bread, tortillas, crackers, and pasta, also fall into this category because the fiber-rich portion of their wheat grain has been removed. Whole-grain breads, pastas, and brown rices are excellent substitutes that allow you to enjoy your carbohydrates without sacrificing the crucial fiber they are naturally packaged with.
Bottom line
Carbohydrate consumption should not be limited, as it is essential for energy homeostasis; however, increased consumption of complex carbohydrates while reducing simple carbohydrates is the most beneficial eating pattern for brain health. Adequate amounts of carbohydrates, or around 55-75% of your daily calorie intake (World Health Organization, 2026), are especially important to the brain health of aging adults because their glucoregulatory and cognition effects magnify over time (Muth & Park, 2021).
Fat
What is fat, really?
To talk about fat, we must first explain the general categories of fat. All dietary fats consist of some combination of saturated and unsaturated fatty acids (including monounsaturated, polyunsaturated, and trans fatty acids). So when we speak of the “saturated fats” found in animal products like butter and steak, we are talking about a fat with a high proportion of saturated fatty acids that is solid at room temperature. Alternatively, unsaturated fats, like olive oil, tend to be liquid at room temperature.
Which fats should I be eating?
Fats have the same dual nature that carbohydrates do: some types of dietary fats are beneficial for brain health, while others can impair brain health. Some of the most crucial fatty acids for brain function are Omega-3 and Omega-6s, which are the two primary structural classifications of polyunsaturated fatty acids, or “PUFAs”. Diets rich in PUFAs have been shown to improve long-term recall, processing speed, and learning and memory (Muth & Park, 2021). PUFAs are most prominent in fatty fish like mackerel, salmon, herring, and sardines. They’re also present in walnuts, flax seeds, chia seeds, and vegetable oils like soybean or canola.
Fats to consume in moderation
High quantities of saturated fats, on the other hand, tend to have the reverse effect of the brain-healthy PUFAs. Saturated fats, in excess, can increase our low-density lipoprotein (LDL), otherwise known as our “bad” cholesterol. Higher LDL, can increase the risk of heart disease and stroke. The health of our cardiovascular system is closely related to the health of our neurological system. Our cardiovascular system is responsible for delivering oxygenated, nutrient-rich blood to our brains. If this system becomes impaired, our brain may not get the oxygen and nutrients it needs to thrive. These effects are often exacerbated by the hyperpalatable nature of saturated fats, which makes them more likely to be overeaten. A high-fat diet typically involves an excess of saturated fats from highly processed, energy-dense foods, rather than an excess of polyunsaturated fats (PUFAs).
What happened to trans fat?
The brain is a fatty organ, composed of around 70% fat (Ginter & Simko, 2016). This means that fats from our diet are incorporated into our brain cell machinery, particularly those involved in nerve signaling. Trans fats disrupt this communication pathway, thereby diminishing mental performance. Accordingly, trans fat consumption has been linked with higher risks of cognitive disorders and cognitive decline as we age (Ginter & Simko, 2016).
Initially, most of the trans fats consumed came from partially hydrogenated oils, a form of vegetable oil manufactured to be solid at room temperature (think margarine and shortening) (U.S. Food and Drug Administration, 2024). Luckily, as of 2021, the FDA has banned artificial trans fats in the American food supply.
Protein
How much is enough?
After sorting through the nuances of carbohydrate and fat intake, the research linking protein to brain health is far more straightforward: adequate protein intake supports memory and cognition! The WHO recommends about 0.8 grams of protein per kilogram of body weight, with values drastically higher or lower than that associated with poorer health outcomes. This correlates to roughly 10-15% of daily total energy intake (World Health Organization, 2026).
As for older adults, 1.2 grams per kilogram body weight daily is frequently cited. This amount promotes bone, muscle, and immune health (Harris, et al., year).
Overconsumption
Depending on the age group or disease state that you fall into, you may be more prone to either over- or under-consumption of protein. For individuals with Chronic Kidney Disease (CKD) in stages 3–5 who are not on dialysis, protein restriction is recommended, as excessive intake may accelerate the progression of kidney dysfunction (Kalantar-Zadeh, 2017). NHANES data suggests that across all stages of CKD, mean dietary protein exceeds recommendations (Moore, 2013). Although overconsumption of protein may be prevalent for those living with CKD, many older adults are not consuming enough!
Underconsumption
Older adults often fall on the opposite end of the spectrum, consuming less protein than what is recommended. This can be due in part to the greater effort required to prepare protein-rich foods, as well as the tougher textures of meats, which may be difficult to chew for those with age-related dental issues. Over 40% of adults ages 70+ consume less than the recommended amount of protein. This number can jump to over 50% in older women (Krok-Schoen et al., 2019). Cognitive difficulties in the elderly may be in part due to this inadequate consumption of protein (Muth & Park, 2021).
Carbohydrates, fatty acids, and proteins are the three macronutrients that make up our diet. Diets that emphasize complex carbohydrates, polyunsaturated fats, and adequate amounts of protein support brain health, whereas those high in simple sugars, saturated fats, trans fats, and imbalanced protein consumption can compromise it. Brain health in this context encompasses memory, learning, recall, processing speed, cognition, and the risk of developing a cognitive disorder. Although all foods can be enjoyed in moderation, being mindful of what we consume can help protect our body’s most vital organ.