Diet high in processed grains such as white bread, white flour and sugar could increase the risk of depression in older women, according to a study conducted by researchers from Columbia University that was published in the American Journal of Clinical Nutrition. In contrast, a diet high in whole grains and vegetables decreases the risk.
Approximately three percent of people in the United Kingdom suffer from depression. In the United States, the proportion of people over the age of 12 suffering from depression is eight percent.
The National Institute of Mental Health characterises the main symptoms of depression as persistent feelings of anxiety, emptiness, guilt, helplessness, sadness, worthlessness, irritability, fatigue or restlessness; difficulty concentrating; changes in sleep patterns; and suicidal thoughts.
Refined carbohydrates such as white flour and white rice are made by stripping away the high-fiber part of the seed. Consequently, these “white carbs” have much higher proportions of simple sugars and are lower in other nutrients. Typically, these foods score higher on the glycemic index, GI scale, a measure of how much sugar is found in the blood after eating a certain food.
In order to compare the influence of different types of food on depression, the researchers collected data on more than 70,000 postmenopausal women who had taken part in the Women’s Health Initiative study between 1994 and 1998. They looked at the types of carbohydrates consumed, the glycemic load from these foods, and the rates of depression.
The researchers found that a higher consumption of sugar and refined grains was linked to a higher dietary GI score, and both of these were associated with an increased risk of new-onset depression. In contrast, women who ate more fiber, whole grains, vegetables and fruit (excluding fruit juice) had a lower risk.
“This suggests that dietary interventions could serve as treatments and preventive measures for depression,” researcher James Gangwisch said.
As a potential explanation for this connection, the researchers noted that the consumption of high GI foods leads to spikes in blood sugar, which then leads to higher insulin levels.
High insulin, in turn, has been shown to worsen symptoms of depression including mood changes and fatigue. Additionally, the researchers remarked that a diet high in refined sugars and grains is associated with a higher risk of inflammation and cardiovascular disease, both of which are depression risk factors.
Other researchers were more skeptical, pointing out that the study was not designed to prove that the high GI diet actually caused the higher rates of depression.
“When you feed your body and brain healthy, whole, nutrient-rich foods, you feel better,” said dietitian and nutrition researcher Lona Sandon of the University of Texas. “You may feel better and have a better mood, simply because you know you are doing something good for your body.”
“What is not clear from the report is whether or not the depression or consumption of refined carbohydrates came first,” Sandon said. “Many people make poor food choices when they are depressed or even stressed, and may reach for refined carbohydrates — like chocolate — in an attempt to improve their mood.”
Another dietitian and nutrition researcher, Penny Kris-Etherton of Penn State University, had a more positive reaction, calling the study “part of an important piece of emerging literature.”
“People are just starting to explore the connection between nutrition and mental health,” Kris-Etherton said. “And I think this work will add fuel to a fascinating area of study, which is certainly worthy of more investigation.”
The researchers themselves acknowledged the limitations of the study and called for more research to confirm their findings in men and younger women.
Many factors can affect a food’s glycemic index, including the following:
• Processing: Grains that have been milled and refined—removing the bran and the germ—have a higher glycemic index than minimally processed whole grains.
• Physical form: Finely ground grain is more rapidly digested than coarsely ground grain. This is why eating whole grains in their “whole form” like brown rice or oats can be healthier than eating highly processed whole grain bread.
• Fiber content: High-fibre foods do not contain as much digestible carbohydrate, so it slows the rate of digestion and causes a more gradual and lower rise in blood sugar. (17)
• Ripeness: Ripe fruits and vegetables tend to have a higher glycemic index than un-ripened fruit.
• Fat content and acid content: Meals with fat or acid are converted more slowly into sugar.
Numerous epidemiologic studies have shown a positive association between higher dietary glycemic index and increased risk of type 2 diabetes and coronary heart disease. However, the relationship between glycemic index and body weight is less well studied and remains controversial.
One thing that a food’s glycemic index does not tell us is how much digestible carbohydrate – the total amount of carbohydrates excluding fibre, it delivers. That is why researchers developed a related way to classify foods that takes into account both the amount of carbohydrate in the food in relation to its impact on blood sugar levels. This measure is called the glycemic load. (11,12) A food’s glycemic load is determined by multiplying its glycemic index by the amount of carbohydrate the food contains. In general, a glycemic load of 20 or more is high, 11 to 19 is medium, and 10 or under is low.
The glycemic load has been used to study whether or not high-glycemic load diets are associated with increased risks for type 2 diabetes risk and cardiac events. In a large meta-analysis of 24 prospective cohort studies, researchers concluded that people who consumed lower-glycemic load diets were at a lower risk of developing type 2 diabetes than those who ate a diet of higher-glycemic load foods. A similar type of meta-analysis concluded that higher-glycemic load diets were also associated with an increased risk for coronary heart disease events.
Here is a listing of low, medium, and high glycemic load foods. For good health, choose foods that have a low or medium glycemic load, and limit foods that have a high glycemic load.
Low glycemic load (10 or under)
• Bran cereals
• Kidney beans
• Black beans
• Wheat tortilla
• Skim milk
Medium glycemic load (11-19)
• Pearled barley: 1 cup cooked
• Brown rice: 3/4 cup cooked
• Oatmeal: 1 cup cooked
• Bulgur: 3/4 cup cooked
• Rice cakes: 3 cakes
• Whole grain breads: 1 slice
• Whole-grain pasta: 1 1/4 cup cooked
High glycemic load (20+)
• Baked potato
• French fries
• Refined breakfast cereal: 1 oz
• Sugar-sweetened beverages: 12 oz
• Candy bars: 1 2-oz bar or 3 mini bars
• Couscous: 1 cup cooked
• White basmati rice: 1 cup cooked
• White-flour pasta: 1 1/4 cup cooked