Jennie writes: I recently heard about something called the cracker test. We did the test in our family and the cracker did not get sweet for any of us. Apparently this means that we should only eat 25% carbs. I’d love to hear your comments.
Raise your hand if you know what the cracker test is. I first learned about it in high school biology, as part of a unit on human digestion.
What Is Salivary Amylase?
Digestion, we learned, begins in the mouth. As you chew your food, it’s mixed with saliva, which contains an enzyme called amylase. This enzyme helps to break large starch molecules down into smaller sugar molecules. Fortunately for those who don’t chew very well, the digestion of starch continues in the small intestine, courtesy of starch-digesting enzymes secreted by the pancreas. In fact, only about 5% of starch digestion occurs in the mouth, so even if you swallow that bite of bagel whole, you’re still going to digest most of it.
Meanwhile, back in high school, the cracker experiment was a fun way to demonstrate the action of salivary amylase.
How Does the Cracker Test Work?
Here’s how to do it at home: take a bite of an unsalted saltine cracker and chew it without swallowing. As you chew, you may perceive a subtle shift in the taste as some of the starch in the cracker is converted into sugar by salivary amylase enzymes. Learning is always more fun when it involves snacks!
But now the cracker test is taking the internet by storm. It’s being promoted as a way to determine how much carbohydrate your body can tolerate. According to proponents, the length of time it takes for the cracker to start to taste sweet in your mouth determines the percentage of carbohydrate your diet should contain. The longer it takes for the cracker to taste sweet, the lower your carb intake should be.
The Evolutionary Role of Salivary Amylase
It’s true that there are genetic differences that affect the amount of salivary amylase we each produce. These differences are thought to be an evolutionary response to different diets. Let me explain: In agricultural societies, where starch intake tended to be higher, natural selection favored genetic variations that led to greater salivary amylase production. Why? Well, if you had more salivary amylase, you’d be able to extract just a little bit more energy out of a high starch diet. In a time when food was not as abundant as it is today, this would be a survival advantage.
Hunter gatherer societies, on the other hand, tended to have a lot less starch in their diets. These societies might still have experienced random genetic variations that resulted in some people having more salivary amylase. But because this conferred little survival advantage, it would not have been selected for in these populations. As a result, someone of Egyptian descent (one of the first places that agriculture flourished) may produce more salivary amylase than someone descended from the indigenous peoples of North America, to which agriculture came much later.
Of course, as we’re all finding out thanks to mail order DNA sequencing, our genetic makeup is a lot more mixed up than many of us realized. You really can’t rely on your last name or the language your great grandparents spoke or even your skin color to know what’s in your genes.
In any case, the cracker test is supposed to be a quick and easy way to determine your salivary amylase levels and, by extension, whether your genes are built to digest bison or baguettes. If it takes a long time for the cracker to taste sweet, it suggests that you have less amylase in your saliva. Therefore, the theory goes, you’d be better off limiting the amount of starch you eat.
Why the Cracker Test Is Crackers
There are are so many flaws in this argument, it’s hard to know where to begin.
I’ll start by saying that the cracker test is not a reliable indicator of your genetic makeup...or even your salivary amylase production. For one thing, the change in flavor is subtle. If you’re expecting that saltine to start tasting like cake, you'll be chewing a long time. Our perception of sweetness is also greatly affected by our customary intake of sugar (and even more so by artificial sweeteners). Someone who rarely consumes sweetened or artificially sweetened foods may be more likely to perceive that subtle sweetness than someone whose taste buds are accustomed to a higher level of sweetness.
Of course, there are more legitimate ways to measure the amount of salivary amylase, but they involve test tubes and reagents, not saltines. Even so, the levels of amylase in your saliva aren’t determined only by your genes.
Salivary amylase levels vary throughout the day; they are likely to be much higher in the evening than in the morning, for example. Psychological stress can also cause a surge of salivary amylase. In fact, researchers often use it as a marker in studies looking at the impact of stress and stress interventions. Caffeine can stimulate salivary amylase production. Smoking and green tea can inhibit it. An increase in body weight can down-regulate amylase production. And so on.
With all of that noise, I don’t think we can use salivary amylase levels as a reliable marker for our genetic disposition to carbs. And even if we could, there’s another glaring logical flaw in this theory.
There are more legitimate ways to measure the amount of salivary amylase.
Let’s say I am descended from hunter-gatherer stock and, as part of that genetic heritage, I have lower salivary amylase levels. As a result, my body’s ability to break down starches is slightly diminished, meaning that I will absorb slightly fewer calories from the starches I eat. Twenty thousand years ago, when food was harder to come by, that may have been a disadvantage. Today, when food is overly abundant and we tend to consume more than we can use, this starts to sound like an advantage. Undigested starch, after all, can also be described as fiber.
Now let’s say that I follow the advice given by proponents of the cracker test. Because I have lower salivary amylase production, I drastically cut down the amount of carbohydrates in my diet, replacing them with the exact same number of calories from protein and fat. Instead of some of the starches from my brown rice and sweet potatoes passing through me undigested, all of the calories from my bone broth and nut butter are being absorbed. In this scenario, I would end up gaining weight! In fact, research has found that, among people with fewer copies of the amylase-producing gene, those who eat more starch tend to weigh less than those who eat lower-carbohydrate diets.
That said, the impact of salivary amylase on starch digestion (and its relationship to body weight) is modest. The vast majority of starch digestion occurs in the small intestine and is unaffected by the genes that determine salivary amylase production.
Finally, keep in mind that starch is not the only type of carbohydrate in our diets. Fruits, vegetables, and dairy products all contain carbohydrates in the form of simple sugars—and these would be unaffected by high or low salivary amylase levels. So, even if the cracker test were a reliable way to determine your genetically-ordained ability to digest starch, the idea that the percentage of carbohydrates in your diet should be dictated by your salivary amylase levels is—in my opinion—completely crackers.
Image of saltine crackers © Shutterstock
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