How sugar impacts immunity
In this article, I’ll be calling out and demonising refined and simple sugars - those found in sweet snacks and desserts, fruit juices and soft drinks. Even honey and maple syrup can be classed as ‘simple’ sugars which, when included in the diet on a regular basis, can prevent the immune system from operating efficiently.
What I won’t be doing is making you feel bad for eating whole fruit, the odd date ball or chia pudding sweetened with stevia. As for other natural sweeteners, coconut sugar is still sugar (though it is less refined and contains fibres which lessen the blood sugar response) and agave syrup should be avoided like the plague. Agave is a highly refined, high-fructose syrup which puts a strain on the liver and contributes to long-term health problems like metabolic syndrome and type 2 diabetes. Sorry if that burst your bubble. Now, on with the article.
Sugar: the bitter truth
In a study looking at the effect of carbohydrates on immunity - specifically glucose, fructose, sucrose, honey and orange juice - participants were given 100g doses of these foods and changes to immune function were observed over 12 hours.
What they found was that suppression of the immune system occurred as quickly as 30 minutes after ingestion of sugar and peaked in the first 1-2 hours. Fructose was the worst contender, reducing the activity of white blood cells by 45%, whereas the other sugars reduced immune activity by around 40%. The effects of 100g doses of sugar - easily obtainable in fruit juices and soft drinks, or a sweetened cup of coffee with a breakfast muffin - lasted for at least 5 hours after ingestion.
One of the ways sugar disables immunity is by blocking the uptake of vitamin C into the cell. Vitamin C acts as a cellular antioxidant, protecting white blood cells against the poisonous free radicals they generate whilst fighting infection. Insulin, a hormone secreted by the pancreas, is known for its role in transporting sugars into the cell - what is less widely known about this hormone is that it is also responsible for the uptake of vitamin C and other nutrients. And when blood sugar is raised - say, after a sugary drink or snack - the uptake of vitamin C is blocked in favour of glucose. The reason this happens is that the sugar molecule is chemically very similar to vitamin C, and they compete for the same receptors. Less vitamin C in the cell means reduced activity of white blood cells, higher rates of cell death and reduced production of new immune cells.
Sure enough, in the above study they found it took a further 5 or 6 hours for vitamin C levels to return to their original intracellular concentrations after consumption of 100g sugar. This means that people who consume simple carbs at breakfast, mid-morning, mid-afternoon and evening are suppressing their immune system all day long and into the night.
Sugar in context
Luckily, slow release low ‘glycaemic index’ (GI) foods and moderate GI carbs, like wholegrains and oats, do not have this effect on immunity. Consuming fat and protein with your carbs will also lower the overall ‘glycaemic load’ (GL) of a meal - a smoothie made with banana, kale, avocado, nuts & seeds has a less pronounced effect on blood sugar than an apple, pear and orange fruit juice, for example.
Stress, sleep, nutrient repletion and activity levels will also modify the picture for each person. During physical activity your body does not require insulin for the uptake of sugar into the cell, so if you’re consuming your chocolate bar in between rounds of star jumps, you’re technically ok.
Equally, someone who has a diet high in organic vegetables, wholegrains, healthy protein and fat, the effects of sugar on blocking vitamin C uptake is not going to be as damaging as for someone who is low in essential nutrients. The overall glycaemic load of your daily diet is also important - if you have cereal and milk for breakfast, a banana mid-morning, a sandwich for lunch and pasta or potatoes for dinner you haven’t necessarily consumed much ‘sugar’, but the high GI carbs soon add up.
So what’s the bottom line? Generally speaking, a healthy person can get away with consuming dessert once or twice a week providing their diet is rich in beneficial phytonutrients most of the time. However, if you’re battling insulin resistance, PCOS, fatigue, acne, breast cancer or virtually any other chronic disease, giving up sugar is the way to go. The good news is that good behaviour begets good behaviour - the less sugar you eat, the less you’ll want to eat. Cutting sugar for just 2 weeks is enough to kick start both your taste buds and metabolism, and set you on the right track to a nutritious diet low in simple carbs.
References
1. Stanhope KL et al (2013) Adverse metabolic effects of dietary fructose: results from the recent epidemiological, clinical, and mechanistic studies. Curr Opin Lipidol. 24(3):198-206.
2. Sanchez et al (1973) Role of sugars in human neutrophilic phagocytosis, The American Journal of Clinical Nutrition, Volume 26, Issue 11, November 1973, Pages 1180–1184.
