Dear Mark: Sugar as Immune Suppressant

Dear Mark,



Since going Primal last summer, my vegan buddy and I have some very explicit differences of opinion. I’m sure you can guess where they come up. Where we agree though is on the subject of sugar, especially refined sugar (syrups, honey, HFCS, table sugar, etc). Neither of us eat the stuff as a rule, but we have different reasons for avoiding it. I give the standard list and his main contention is that sugar compromises the immune system. Is this true? Does eating sugar actually suppress the immune system? I’ve heard this before, but have yet to see hard proof. Thanks.

Thanks for the question. We already know sugar should be limited in the human diet. Most people can agree with that. Here are but a few of its effects on our physiologies. Fun stuff!

It leads to insulin resistance.

It promotes inflammation in the body.

It can lead to weight gain when ingested.

It contributes to non-alcoholic fatty liver disease. In fact, our livers process fructose very similarly to the way they process ethanol. Lustig calls fructose “alcohol without the buzz.”

It appears to act like fertilizer for cancer cells.

High fructose diets decrease HDL levels, while reducing the diameter and increasing the density of LDL particles.

Glucose and especially fructose can bond to – glycate – proteins and lipids without proper enzymatic control.

All that would be plenty justification for anyone to cut sugar from their diet, wouldn’t you agree? I mean, who wants glycated lipids wedging themselves between endothelial walls, or a cascade of inflammatory responses leading to weight gain and insulin resistance, or a bed of happy, hungry cancer cells enjoying a steady supply of food? Not me.

But you were wondering whether sugar really suppresses the immune system. It’s a charge often levied against the humble ivory granules, and, perhaps owing to their despicable record, it’s stuck. Sugar is an easy target to pick on, and it’s a sticky substance (at least when wet), so things stick.

As to whether sugar directly impacts the immune response, there is evidence that it does play a role: the often-cited 1973 neutrophilic phagocytosis study out of Loma Linda University. Neutrophils are small white blood cells, about 9 or 10 µm in diameter. They’re also the most abundant white blood cell, or leukocyte, in the body. Good thing, too, because they play a crucial role in the defense of the multicellular organism (that’s us). Neutrophilic phagocytosis is the process by which offensive microbes are dispatched by neutrophils.

The Loma Linda study observed the effect of sugar ingestion upon neutrophilic activity. After an overnight fast, subjects were administered oral 100 gram portions of either glucose, fructose, sucrose, honey, or orange juice. Blood was drawn before and after administration of the sugar, then mixed with a shot of staphylococcus epidermidis (a fairly common bacterial strain that can be virulent in compromised immune systems) to determine the neutrophilic phagocytosis response. After ingestion of sugar (but not starch), the phagocytic index (a rough measurement of the neutrophilic response) was significantly decreased, while fasting significantly increased the response. Sugar eating didn’t decrease the number of neutrophils; it simply decreased their responsiveness.

It isn’t exactly clear that sugar and sugar alone exerts a neutrophilic-dampening effect on our immune system. I’m inclined to think that the neutrophils aren’t lying dormant, befuddled and entranced by the fructose. Instead, I’m thinking they’re occupied by the rapid influx of twenty teaspoons of sugar into the body. Let me rephrase that: they’re occupied by the effects of the rapid influx of sugar. To understand what I mean, look at the start of this post. Check out all those negative, inflammatory effects sugar has on our body, and think about how twenty teaspoons of sudden sugar might necessitate an inflammatory response to deal with them all.

Who’s well-represented among the first wave of the inflammatory response, you might ask? Neutrophils. They are often the first responders to migrate toward the site of inflammation. Now, if a rapid influx of sugar can provoke an inflammatory response, and if that inflammatory response consists of neutrophils springing into action, it might explain the results of the Loma Linda study. Perhaps the neutrophils were dealing with the sugar rush. Maybe their cytoplasmic storage granules, which usually contain antimicrobial weaponry, were depleted after handling the fallout from all that fructose. In any case, though the Loma Linda study is suggestive, more research needs to be done on sugar and its possible immune suppressing effects.

What we do know is that it’s impossible (and shortsighted) to hone in on just a single factor. It isn’t just sugar that suppresses the immune system. It’s also stress. It’s too little exercise, or too much. It’s lack of sleep. It’s the SAD. Whatever contributes toward chronic inflammation, weight gain, excessive cortisol, and the metabolic syndrome is most likely also contributing to the compromised immune system. Sugar plays a role, maybe even a big one, but it’s not the only player.

We also know that people following the Primal Blueprint appear to be healthier. They’re the ones who survive flu season with nary a scratch, while their office mates take sick days and the trash bins overflow with used tissues. When they do fall ill, the turnover is quick and painless. These may just be anecdotal accounts, but they’re extremely powerful. Is it because of sugar avoidance? Seems likely. Whatever it is, though, it’s working.

So, sorry, Poppins. Keep your spoonful of sugar. It may very well help your spoiled wards choke down their medicine, but it could also make the problem – a weak immune system – even worse.

What are your thoughts? Have you noticed fewer colds and flus since ditching sugar and going Primal? Share your stories in the comment board!





About the Author Mark Sisson is the founder of Mark’s Daily Apple, godfather to the Primal food and lifestyle movement, and the New York Times bestselling author of The Keto Reset Diet. His latest book is Keto for Life, where he discusses how he combines the keto diet with a Primal lifestyle for optimal health and longevity. Mark is the author of numerous other books as well, including The Primal Blueprint, which was credited with turbocharging the growth of the primal/paleo movement back in 2009. After spending three decades researching and educating folks on why food is the key component to achieving and maintaining optimal wellness, Mark launched Primal Kitchen, a real-food company that creates Primal/paleo, keto, and Whole30-friendly kitchen staples.

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