Best nutrition tips to support your immune system this winter, according to a dietitian

Welcome to Ask A Dietitian, a series where Yahoo Canada digs into food trends and popular nutrition questions with registered dietitian Abbey Sharp.

This article is for informational purposes only and is not a substitute for professional medical advice, diagnosis or treatment. Contact a qualified medical professional before engaging in any physical activity, or making any changes to your diet, medication or lifestyle.

As the winter chill settles over Canada, it's important to help your immune system against seasonal illnesses.

But what exactly should you be eating this season and what dietary habits can help keep your immune system robust? According to Canadian dietitian Abbey Sharp, we can't exactly "boost" our immune system through food, but we can support its optimal functioning with key nutrients.

Here's what you need to know.

What foods help support the immune system?

Sharp highlighted several foods and nutrients that play a key role in supporting a healthy immune system.

She explained 70 per cent of our immune system is in the gut, so "we need a healthy gut if we want a healthy immune system."

These include:

• Fatty fish: known for heart-healthy omega-3s and enhances the activity of white blood cells

• Colourful fruits and vegetables: high in vitamin C, vitamin K, and beta-carotene (crucial antioxidants)

• Zinc: an antioxidant found in nuts proven to be beneficial

• Fermented foods: promote a robust gut microbiome — essential for overall immune health

• High-fibre foods: acting as prebiotics, they feed the good bacteria in the gut

Specifically, the following prebiotic foods can help your gut and immune system: sauerkraut, kefir, yogurt, pickled products, whole grains, nuts, seeds and legumes.

Vitamin D is also important in the wintertime. Sharp explained D3 plays a "critical role" in the functioning of T cells, B cells and dendritic cells, "which are all really important for immune function and to protect you from disease." However, this vitamin isn't found in many foods, so a D3 supplement is recommended — "especially in the dead of winter, when a lot of us are not getting a lot of direct sunlight."

What else can I do to support my immune system?

Exercise is a crucial part of protecting your immune system, according to Sharp.

"We know that getting outside getting movement is a great way to, really, stimulate the immune system," she said.

"This is one of the reasons why even after getting a vaccine, for example, they often recommend you go for a walk or get a little bit of physical activity."

The expert added sleep is "so important for recovery and for reducing cortisol levels and stress levels."

What seasonal foods should I incorporate into my diet this winter?

To help support your immune system in the winter, Sharp recommends embracing seasonal produce.

Citrus (grapefruit, mandarins, clementines, kumquats) are a "great" choice. Pomegranates are too, as they're "full of antioxidants." Leafy greens like kale can be a good source of vitamin K, while sweet potatoes, squash and carrots can provide beta carotene. Proteins like turkey also play a crucial role in the immune system.

"Really, we're just talking about colour," Sharp said.

She also added though berried aren't in-season and can be expensive, frozen berries can be a great addition to variety in your diet.

How can I use winter produce in my daily meals?

To simplify the incorporation of immune-supportive foods into daily meals, Sharp recommended a "count colours, not calories" approach.

Aim for at least three different coloured foods daily. "That could mean like apples at breakfast, a dark leafy green at lunch and a sweet potato, or orange vegetable at dinner," she explained.

And, try to add in at least one probiotic each day, such as from yogurt, fermented foods and a supplement.

"Ultimately, we're never going to get a clinical dosage of probiotics from yogurt. All those things are really great and help — but for a lot of folks, a probiotic supplement can be really helpful."

Are there any diets to avoid in the wintertime?

According to Sharp, there are a few diets she wouldn't recommend this time of the year, as certain dietary restrictions can compromise the immune system.

Diets low in colourful fruits and vegetables, such as strict carnivore or keto diets, may lack essential antioxidants, hindering immune function. Additionally, low-calorie diets, especially when combined with excessive exercise, can elevate cortisol levels, leading to immune suppression.

Sharp advised against extreme dieting and emphasized the importance of a well-rounded, nutrient-dense diet. "We really want to be mindful that we are getting a wide range of nutrients in and those antioxidants in, especially on these low-calorie diets... because it does put a lot of stress on the body."

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