Cutting back on saturated fat and refined sugar may do more than lower your risk of high cholesterol, heart disease and Type 2 diabetes. It may also cut the risk of developing memory problems that could advance to Alzheimer's disease.
According to a study published Monday in the journal Archives of Neurology, a low saturated fat/low glycemic index diet can reduce the concentration of a protein in the brain linked to Alzheimer's disease. A high saturated fat/high glycemic index diet, on the other hand, can increase the amount of this protein.
The glycemic index measures how quickly your blood glucose (sugar) rises after eating a carbohydrate-rich food. High glycemic foods such as white bread, white rice, table sugar and soft drinks cause rapid spikes in blood glucose and insulin, the hormone that lowers blood glucose.
Conversely, low glycemic foods, which include steel-cut oats, brown rice, sweet potatoes, yogurt and apples, are converted to blood glucose slowly and don't cause an influx of insulin.
Previous research has hinted that saturated fat (e.g. meat and dairy fat) increases the risk of Alzheimer's disease whereas replacing it with healthier fats, such as olive oil, has a protective effect.
A diet heavy in both saturated fat and refined carbohydrates (e.g. white starches and sugar) is also linked with a greater risk of insulin resistance and Type 2 diabetes, known risk factors for Alzheimer's disease.
Insulin resistance is a condition in which the body - and brain - cannot properly use insulin. It's thought diabetes and insulin resistance accelerate the build-up of plaque in the brain, a process that underpins Alzheimer's disease.
In the study, researchers gave 49 adults in their mid-60s one of two diets designed to affect insulin levels and insulin resistance: a high saturated fat/high glycemic diet (dubbed as the "high" diet by the researchers) and a low saturated fat/low glycemic diet (or "low"). The objective was to see how each diet affected levels of biomarkers for Alzheimer's disease in the brain.
A biomarker is a substance indicative of the disease. In this case, researchers measured the concentration of a beta amyloid 42, a sticky protein linked to Alzheimer's. Beta amyloid is the main component of the plaques found in the brains of individuals with Alzheimer's disease.
Among the participants, 20 were healthy older adults and 29 had mild cognitive impairment. (Individuals with mild cognitive impairment have memory problems not severe enough to warrant a diagnosis of Alzheimer's disease but they are at increased risk of progressing to the disease.)
As expected, the high diet increased insulin, insulin resistance and LDL (bad) cholesterol in healthy and memory-impaired participants while the low diet had the opposite effect.
In healthy adults the high diet increased the concentration of the beta amyloid 42 protein whereas the low diet reduced it.
The results were different for individuals with mild cognitive impairment. The high diet had no effect on this biomarker while the low diet actually increased it.
As well, the low diet improved performance on certain memory in both groups of participants.
The findings indicate that for healthy adults, a diet high in saturated fat, refined starches and sugars can move Alzheimer's biomarkers in a direction that may reflect a presymptomatic stage of the disease. They also suggest that dietary changes are not as effective at later stages of cognitive impairment.
Since Alzheimer's changes can begin many years before symptoms start, now is the time to modify your diet. Eating a variety of healthy, nutrient-rich foods while minimizing your intake of foods that may harm the brain can help guard against Alzheimer's disease.
Limit saturated fat
Choose lean cuts of meat, poultry breast and low-fat milk and yogurt (1-per-cent milk fat or less). Buy part skim or skim milk cheese.
Use butter sparingly. Prepare foods with unsaturated fats such as olive oil, canola oil, grape seed oil, sunflower oil and non-hydrogenated margarine.
Snack on a small handful of nuts each day; they provide unsaturated fat and vitamin E, an antioxidant that helps shield brain cells from free radical damage.
Choose low glycemic
At meals and snacks choose carbohydrate-rich foods that cause your blood glucose to increase gradually rather than quickly.
Foods with a low glycemic index include grainy breads with seeds, steel-cut and large-flake oats, 100-per-cent bran cereal, brown rice, wild rice, sweet potatoes, pasta, apples, citrus fruit, grapes, pears, legumes, nuts, milk, yogurt and soy milk.
These natural compounds are thought to protect the brain through their antioxidant and anti-inflammatory actions. In animal research, polyphenols have been shown to remove toxins that can interfere with brain function.
Excellent sources include acai berries, blackberries, blueberries, strawberries, raspberries, cherries, cranberries, plums, pomegranate seeds, prunes, red and purple grapes and walnuts.
Include leafy greens. While eating more vegetables in general has been connected to a slower rate of cognitive decline, leafy green vegetables appear to offer the greatest protection, likely because of their vitamin E content.
Leafy greens include arugula, spinach, kale, Swiss chard, beet greens, collard greens, mustard greens and rapini.
Eat more fish
Several studies have reported that fish eaters have a lower risk of Alzheimer's disease and cognitive decline.
Oily fish such as salmon, trout, sardines, mackerel and herring are an excellent source of DHA, an omega-3 fatty acid that helps keep the lining of brain cells flexible so memory messages can pass easily between cells. Omega-3 fats also have anti-inflammatory effects in the brain.
The ideal intake of DHA for brain health is unknown, but experts suggest a daily intake of at least 500 milligrams of omega-3 fats from fish for heart health - an amount that can be obtained by eating six ounces of salmon each week. If you don't like fish, consider taking a fish oil capsule.
Leslie Beck, a Toronto-based dietitian at the Medcan Clinic, is on CTV's Canada AM every Wednesday. Her website is lesliebeck.com.