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Dr. Tim Says....

How the Standard American Diet (SAD) affects the brain

Part One | Part Two

a fast food hamburger meal with french fries

The agricultural and industrial revolution made fats and sugars more available and affordable, leading to a typical American diet that is high in fat and refined carbohydrates (high in sugars and simple starches) and low in complex carbohydrates and fiber. Low fruit and vegetable intake have also contributed to the reduction in the amount of fiber in American diets.

Because of the convenience and low cost of processed foods, many convenience food items produced in mass quantities are high in chemical content. Sodas, potato chips, packaged sweets, etc. all have large amounts of preservatives, artificial food colorings, and other highly processed ingredients that have all been shown to be detrimental to our brains when consumed in large amounts. Similarly, the explosion of fast food restaurants, the decline of traditional sit down family meals, and an emphasis on the convenience factor have all contributed to rising obesity rates in the US.

There has been a clear rise in overweight and obesity over the past 30 years:1
72% of men and 64% of women are overweight or obese
32% of children and adolescents are overweight or obese

The standard American diet has contributed to an increasing incidence of cardiovascular disease, hypertension, type 2 diabetes, and obesity. Physical inactivity, larger portion sizes, and increased screen time - whether television or computer screens - are other lifestyle factors contributing to this unhealthy trend in growing waist sizes.

Glucose Dysregulation and Neurocognitive Decline

Obesity, metabolic syndrome, and diabetes are all examples of dysregulated glucose states (when the body does not use or process glucose correctly). Chronic high glucose levels and excess insulin levels induce a pro-inflammatory state in the body which disrupts normal biochemical processes.2 This stressed state stimulates an overproduction of reactive oxygen species leading to oxidative stress. This pro-inflammatory state impairs the mechanisms in the body that control immune response and has been shown to cause alterations in brain signal processing. The hippocampus (the brain's memory formation and processing center) is particularly susceptible to glucose mismanagement and decreases in volume and structure have been found in brains of patients with high serum glucose.3

The impairment associated with chronic diabetes extends beyond neurocognitive decline to an increased risk of Alzheimer's Disease. Chronic excess insulin levels has been associated with impaired ability to clear amyloid beta proteins (which are the main component of the plaques in the brain typifying Alzheimer's Disease) from the body and damaging the brain's ability to regulate signals between brain cells - both pathologic features of Alzheimer's Disease.4

The accumulation of amyloid beta proteins and impaired signaling between brain cells are linked to accelerated brain aging, which appears as microangiopathy (capillaries that are so weakened that they bleed or leak proteins into the surrounding tissue) and is detected by MRI as white matter high intensity lesions. These lesions, along with other structural changes, have been found to occur at higher rates in diabetic vs. non-diabetic populations.5

A recent systematic review of the literature showed that poor glucose control, as evidenced by hyperglycemia, high hemoglobin A1c levels, and wide glucose fluctuations are associated with poorer cognitive scores in Type 2 diabetics without dementia.6

Choosing Smart Carbohydrates

With impaired glucose management, whether it is obesity, metabolic syndrome, or Type 2 diabetes, being so closely linked with neurocognitive decline and the onset of Alzheimer's, it's important to take charge of our food choices, beginning with choosing smart carbohydrates. Cutting down on the amount of simple, refined sugars that are nutrient poor (such as white rice, grits, and sugar-laden foods) and being conscious about choosing complex carbohydrates that are also higher in fiber content (such as brown rice, oatmeal, fruits, and green leafy vegetables, as well as legumes) will prevent our bodies from becoming subjected to sudden glucose and insulin spikes.

Simple Carbohydrates Replace with Complex Carbohydrates
Soda, fruit drinks, sweet tea + coffee Water, seltzer water, unsweetened or artificially sweetened tea and coffee
Candy, cookies and pastries Nuts and unsweetened fruit
(fresh, dried, canned in juice)
Chips Nuts and seeds
French fries, white pasta, white rice Brown rice, wild rice, faro, bulgur, soba, and whole grain pasta
White bread, rolls, crackers 100% whole grain bread and
seeded bread crumbs
Refined and sugary cereals Oatmeal, whole grain cereals, granola
Meat Beans and lentils

High Fat Diets and Poor Cognitive Health

Diets high in saturated fats have been linked to impairments in cognitive functions, specifically functions involving memory, speed and flexibility in both the short term and the long term.7 In one study, men were given either a 17% fat diet or 74% fat diet. After 7 days, those consuming the high fat diet had significantly decreased attention scores.8 In another study, high saturated fat intake has been linked to decline in memory, processing speed, and attention measures over a six year period.9

Multiple studies have linked increasing ADHD rates with an increased intake of the Western diet: one high in total and saturated fats and simple sugars. When recent CDC prevalence maps of ADHD and obesity rates by state were compared side by side, there is a startling parallel between the most obese states and those with the highest percentages of children ever diagnosed with ADHD.10


1. Ogden et al. "Prevalence of Overweight, Obesity, and Extreme Obesity Among Adults: United States, Trends 1960-1962 Through 2007-2008" June 2010.

2. Roriz-Filho et al. "(Pre)diabetes, brain aging, and cognition." Diabetes and the Nervous System 2009;1792(5):432-443

3. Kerti et al., "Higher glucose levels associated with lower memory and reduced hippocampal microstructure." Neurology 2013;81:1746-52

4. Roriz-Filho et al. "(Pre)diabetes, brain aging, and cognition." Diabetes and the Nervous System 2009;1792(5):432-443.

5. Akisaki et al. "Cognitive dysfunction associates with white matter hyperintensities and subcortical atrophy on magnetic resonance imaging of the elderly diabetes mellitus Japanese elderly diabetes intervention trial (J-EDIT)." Diabetes Metabolism Research and Review 2006; 22:376-384.

6. Geijselaers et al. "Glucose regulation, cognition, and brain MRI in type 2 diabetes: a systematic review." Lancet Diabetes Endocrinology 2015; 3:75-89.

7. Barnard et al. "Saturated and trans fats and dementia: a systemic review." Neurobiology of Aging 2014; 35(2): S65-S73.

8. Edwards et al. "Short-term consumption of a high-fat diet impairs whole-body efficiency and cognitive function in sedentary men." The FASEB Journal. March 2011, Vol 25.

9. Morris et al. "Dietary fat intake and 6-year cognitive change in an older biracial community population." Neurology 2004;62(9):1573-9.

10. Howard et al. "ADHD is Associated With a 'Western' Dietary Pattern in Adolescents." Journal of Attention Disorders 2011;15:403.

Timothy S. Harlan, MD, FACP, CCMS
Dr. Gourmet