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When it comes to kids and flu, low nutrition has profound impacts. Flu, covid, and other viral illnesses draw hard on anyone’s immune resources, and this is especially true for kids. Decades of published literature on this classic corner of nutrition’ show that for kids, being underweight, overweight, anemic, or marginal / lacking in particular nutrients greatly escalates their odds for getting illnesses like flu, getting more complications with flu and other infections, and getting sick more frequently.

In fact, low nutrition is so powerful a driver in children that it can be deadly. Once a child lapses into a repetitive cycle of malnutrition and infection, it can be hard to reverse without focused and swift intervention. Malnutrition and recurrent infections synergize each other, ultimately stunting growth and delaying development. Here’s why: Malnutrition drops the body’s capacity to build and repair itself, while infections boost demand for nutrients that enable immune function. It’s a double-whammy-detrimental-cycle where malnutrition corrupts growth, and stunted growth further perpetuates the malnutrition. Believe it or not, this malnutrition and infection pattern affects many kids right here in the US, and I see it often in my pediatric nutrition practice.

If this happens early in life – during critical periods of development between ages zero to three or five years – poor diets and missing nutrients can have long-lasting cognitive and developmental effects on children. The brain needs adequate nutrition to develop, and infections can worsen cognitive impairments by disrupting the normal progression of neuron growth.

Here in the US, where we have access to more food than we truly need, we are not immune to poor nutrition: Poverty hovers around 12-13% of our population, meaning that some 38 million citizens probably don’t have enough to eat. Still others live in food deserts where there are no supermarkets selling whole foods, or live on fast food or packaged processed snack food that is cheap and lacking in real nutritional value. Even families I work with in my pediatric nutrition practice who can buy good groceries struggle too, with severe picky eaters who don’t eat healthy diets. Still other families I meet have placed their children on unnecessarily restricted diets out of fear for “bad” food – only to see their children have not grown well, get sick more, don’t sleep as well, and are unhappy or anxious. Not enough food and marginal nutrition will do that to kids.

Here’s what low nutrition will do:

  1. Sputtering Overall Immune Response: Malnutrition will drop levels of essentials like vitamin A, C, and D, iron, zinc, and macronutrients like protein. These nutrients are literally crucial for the proper functioning of the immune system. When a cold or virus comes calling, your child’s immune system will recruit those nutrients to build a good response – if there are enough of them around. If these are marginal or lacking, illness ensues. Kids need good digestion and absorption, plus good food sources of these nutrients, to stay well. Supplements can help, but can’t work if there isn’t enough good food to allow for growth and gain at the same time.
  2. Weakened Antibody Production: Antibodies are proteins that neutralize bacteria and viruses. Whether triggered by a vaccine or by a wild type infection, the body will respond with an effort to make antibodies. Low protein intake can hinder the body’s ability to generate antibodies, making it harder to fight infections or tolerate vaccines normally. To spare protein for tasks like antibody production, children need good total diets with all macronutrients, including carbohydrates and starches. Otherwise, protein is burned as fuel and wasted. Too little protein in the diet – as well as too much protein without enough starches – can have harmful effects for kids.
  3. Impaired T-Cell Function: T-cells are white blood cells that play a central role in the immune response. They help identify and destroy infected or abnormal cells. Malnutrition reduces number of T-cells and impair their ability to function effectively.
  4. Weakened B-Cell Response: B-cells are another type of white blood cell that produce antibodies. Malnutrition can impair the development and maturation of B-cells, dropping an effective antibody-mediated immune response.
  5. Decreased Phagocytosis: Phagocytes are specialized immune cells (like neutrophils and macrophages) that engulf and destroy pathogens. Malnutrition can reduce their effectiveness, making it harder for the body to clear infections.
  6. Poor Wound Healing: Low nutrition weakens skin and mucosal barriers, which serve as our first line of defense against pathogens. Just being underweight will weaken the gut wall and cause leaky gut, making it easier for pathogens to enter the bloodstream. Weakened barriers means delayed wound healing, increased risk of infections, easier penetration of pathogens in lung, gut, or even brain. In my practice, I work with families so that children can maintain a body mass index above tenth percentile for more robust health.
  7. Altered Gut Microbiota: Total food intakes below a child’s needs, and/or un-varied, picky diets, disrupt the balance of beneficial bacteria in the gut. This negatively impacts the immune system, as a healthy gut microbiota is crucial for regulating immune responses.
  8. Decreased Energy Reserves: Underweight children have limited energy reserves, which compromise the body’s ability to mount a robust immune response. The body may prioritize essential functions like maintaining body temperature over fighting infections.
  9. Increased Susceptibility to Infections: Malnourished children are more susceptible to a wide range of infections, including respiratory tract infections, gastrointestinal infections, and opportunistic infections.
  10. Long-Term Impact: Chronic malnutrition during critical periods of growth and development can have long-lasting effects on the immune system. This can lead to a higher risk of infections and other health problems throughout the child’s life.

What to do… Feed your kids ample portions. I meet many parents who fear carbs, starches, or other foods and inadvertently over-restrict their kids. If your child is past the age of 1 or 2 years and can’t reliably sleep through the night, this is one sign that they need more to eat. Allow bedtime snacks, and include all macronutrients: Some carbs, some protein, and some fats. Unless your child is overweight with a body mass index above the 90th percentile, there is no need to restrict food intake.

Don’t let your kids graze after age 15-18 months. Grazing and sipping work for babies, but past infancy, this starts to backfire. Organize distinct meals and snack times. Grazing reduces appetite overall, engenders gut dysbiosis especially in the small intestine, and tends to stall growth patterns.

Allow starches and carbs. Healthy clean carbs diversify the gut microbiome, feed your child’s brain with its preferred fuel (glucose) and allow for normal bone mineralization. Carbs do this by sparing protein for other tasks like building tissue, growing, and making functional molecules like immune proteins, hormones, or neurotransmitters. About half your kids’ food should be from starches and carbs. Think whole grains (whatever are tolerated), quinoa, sweet potato or potato with skins, asparagus, green beans, Pinto beans, black beans, organic corn or cornmeal, squashes, any veggies or fruits. Sweets can work too in moderation. For low or no sugar sweets or recipes for treats with honey, check my recipe blog here.

Have your pediatrician do an iron study to see if your child needs iron support. Iron is a critical player in immune response. Include vitamin D level, a complete blood count (CBC), and serum zinc in the blood work too, if your doctor will allow it. Supplement if findings warrant it. Look for a vitamin D level between 60-80, for good protection.

Use vitamin A foods generously. Vitamin A itself is only found in animal foods like egg yolks, grass fed butter, cod liver oil, or calves’ liver. Plant sources require conversion for metabolically active forms of vitamin A used by the immune system. Use all of these foods liberally, from carrots, yellow bell peppers, and mangoes to bright orange yolks.

Though they don’t replace good food for best support, multivitamins can help if your child is unable to eat all these wonderful, nourishing foods day to day. But, kids still need enough total food and a balance of macronutrients (carbs, protein and fats) to make supplements really work.

Use probiotics. These have been shown to protect against upper respiratory infections.

When I work with families on building strong  nutrition status for kids, parents are simply amazed when kids navigate a flu season with nary a flu, covid, or barely a cold. I have seen this happen many times in my pediatric nutrition practice. While it’s typical for kids to get sniffles, good nutrition status means they will be able to mount a fever if necessary, rebound swiftly, and carry on. Expect your kids to feel well – they can! For tips on how to support fever with nutrition measures, check out this blog post too.