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food for thought

Leslie Beck, a Toronto-based private practice dietitian, is director of food and nutrition at Medcan. Follow her on Twitter @LeslieBeckRD

Recommendations for healthy eating are the same for males and females. Eat fruit and vegetables, whole grains, healthy proteins and limit sodium, added sugars and saturated fat.

When it comes to individual nutrients, though, daily requirements aren’t always similar owing to differences in sex hormones.

Menstruating women need more iron than men do, for example. And with the loss of estrogen that occurs with menopause, a woman’s daily calcium requirement increases to help guard against osteoporosis.

According to researchers from the University of Georgia, there’s another dietary component that females need to be proactive about: carotenoids. That’s especially so when it comes to guarding against cognitive decline and vision loss. Here’s why, and how to consume more of them.

Sex differences in eye and brain health

While females tend to live longer than males, they are more vulnerable to diseases and conditions that, while not always life-threatening, are debilitating. Cataract, macular degeneration and dementia, for instance, affect females more often and sooner than males.

The review of research, published June 11 in the journal Nutritional Neuroscience, states that females represent 70 per cent of all cases of dementia, most notably Alzheimer’s dementia, and age-related macular degeneration.

Reasons include hormonal differences, genetic variations and/or differences in the generation of inflammation and oxidative stress. Oxidative stress occurs in the body when there is an imbalance between free radicals and antioxidants. When left unchecked, free radicals can damage cells and tissues.

Carotenoids: a focus on lutein

In the new review, the researchers contend that higher rates of neurodegenerative illnesses among females could be reduced by eating a diet high in carotenoids, phytochemicals that have potent antioxidant and anti-inflammatory effects.

Watermelon is a source of lycopene.Getty Images/iStockphoto

Carotenoids in our diet include beta-carotene (e.g., carrots, sweet potato, mango, spinach), lutein and zeaxanthin (e.g., spinach, kale, Swiss chard), lycopene (e.g., tomato sauce, tomato juice, watermelon) and beta-cryptoxanthin (e.g., pumpkin, papaya, red bell pepper).

Lutein and zeaxanthin are the only carotenoids found in the eye; they’re concentrated in the macula, the central part of the retina that controls fine detailed vision. Here they protect the eye tissues from light-induced free radical production. Lutein and zeaxanthin are also the primary carotenoids found in the brain.

Many studies have linked higher intakes of lutein and zeaxanthin to a lower risk of macular degeneration and cataract. Studies conducted in children, young adults, older adults and adults with cognitive impairment all suggest that an increased intake of lutein and zeaxanthin improves brain function.

What is the recommended daily intakes for lutein?

Unlike vitamins and minerals, there aren’t official recommended daily intakes for phytochemicals, including carotenoids. Evidence from observational research, however, suggests that a daily intake of 3 to 5 mg of lutein and zeaxanthin protects against early, intermediate and advanced age-related macular degeneration.

A 2020 study, published in the American Journal of Clinical Nutrition, found that a daily intake of 25 mg of total carotenoids was tied to a lower risk of Alzheimer’s disease in older adults. High intakes of lutein and zeaxanthin were especially protective.

Interestingly, the latest research review suggests that females require more carotenoids than males to protect against disease. One reason has to do with how they’re stored in the body.

Carotenoids, which are fat soluble, are stored in adipose tissue. Females have, on average, more body fat than males. Research has shown that, despite similar intakes and blood levels of lutein and zeaxanthin, females have higher levels of them in their adipose tissue than do males.

These stores are useful during pregnancy and breastfeeding. But, according to the researchers, it also means that less lutein and zeaxanthin is available for the eye and the brain, putting women at greater risk for degenerative problems later on.

They conclude that “given the high probability of help and the low probability of harm, targeting the lutein and zeaxanthin intake of women is a wise strategy.”

What are the best food sources for lutein?

Exceptional sources of lutein and zeaxanthin are cooked leafy greens including spinach (15 mg per one-half cup), kale (12.5 mg), Swiss chard (9.5 mg), collards (9 mg), dandelion greens (5 mg) and mustard greens (4 mg). These vegetables also provide a decent amount of beta-carotene.

victoriya89/Getty Images/iStockphoto

Other sources of lutein and zeaxanthin are summer and winter squash, green peas, Brussels sprouts and broccoli. Egg yolks and avocado are low buy highly bioavailable sources of lutein and zeaxanthin thanks to their fat content.

Be sure to include a little fat in your meal (e.g., two teaspoons of oil) to optimize the absorption of carotenoids.

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