The other day, I came across something called the cracker test.
It’s a 30-second test that (supposedly) tells you if carbohydrates make you fat – and if you should cut down or eat more.
In short, the cracker test is supposed to tell you how much amlyase – the enzyme that initiates starch digestion – you have in your saliva.
The length of time it takes to detect a change in taste will place you in one of three carbohydrate consumption categories – full, moderate or restricted.
The Cracker Test Explained
Here’s how Xand van Tulleken, a medical doctor and presenter of the BBC TV documentary The Truth About Carbs, explains it:
“The idea is that you chew on a plain cracker until it changes in flavor from a bland biscuit to quite sweet.
“If the taste changes in less than 30 seconds, your body probably processes carbs quite effectively.
“But if the cracker hasn’t changed taste after 30 seconds, then you should seriously consider eating a lower carb diet.
“If you notice the sweetness within 0 to 14 seconds, your body processes carbs efficiently for use as energy — you can have 250 grams of carbs a day (for women) and 325 grams of carbs a day (for men).
“If it takes 15 to 30 seconds, you can have 175 grams of carbs a day (for women) and 230 grams a day (for men).
“More than 30 seconds, you’re not a great processor of carbs so the body is less able to use the excess as energy, and so stores it as fat. You can have 125 grams of carbs a day (for women) and 165 grams a day (for men).”
The Truth About Carbs
In The Truth About Carbs, van Tulleken tried the cracker test with a group of students.
Each student was told to chew an unsalted cracker for 30 seconds, and raise their hand when they detected a change in taste.
The student who noticed a change in the shortest time raised their hand after 17 seconds. Some said they didn’t notice any change.
According to van Tulleken:
“Seventeen seconds is quite fast. This suggests you have a high concentration of amylase enzymes in your mouth which are chopping up the big starch molecules into smaller molecules of sugar or sugar-like molecules that you can taste.”
For those who didn’t notice a change a taste, Van Tulleken says they have a low concentration of salivary amylase, and shouldn’t eat as many carbs.
Here’s a video of some people eating crackers if you want to watch:
Can the Cracker Test Tell You How Many Carbs to Eat?
To me, the whole thing had more than a faint whiff of BS about it.
But, I had nothing better to do, so I tweeted van Tulleken to ask if he knew of any research that supports the use of the cracker test.
He didn’t reply, so I took a dive into the research to see what I could find.
The first reference to the cracker test I found was in a 2016 book by geneticist Sharon Moalem called The DNA Restart: Unlock Your Personal Genetic Code to Eat for Your Genes, Lose Weight, and Reverse Aging.
For some people carbs are beneficial, Moalem says, because they come from ancestors who relied heavily on starches, farmers who grew and consumed cereal grains.
They have inherited multiple copies of the gene that the body uses to make salivary amylase, called AMY1.
Some people have as many as 20 copies of the gene and can digest a lot of starch, while others have fewer copies or even none and will have problems digesting it.
“It’s an amazing enzyme because it has the ability, within seconds, to start breaking down starch,” says Dr Moalem.
“It’s like a giant pair of shearing scissors that can cut apart big and bulky starch molecules into simpler sugars. The faster it cuts up the starch into simpler sugars, the more carbohydrate you can handle without gaining fat.
Does Moalem present any evidence to show that the cracker test is a reliable way to establish what your daily carb intake should be?
If he did, I couldn’t find it.
In fact, there was nothing in the book to show that the speed at which a cracker changes in flavor from bland to sweet has any predictive value when it comes to deciding what your daily carb intake should be.
The main premise of the cracker test is that people with low levels of salivary amylase will take longer to notice a change in taste. They’re the ones who are supposed to place the greatest restrictions on the amount of carbohydrate they eat.
However, one study I came across, published in the American Journal of Clinical Nutrition, pours cold water on the idea.
The study, which looked at a group of 4800 individuals from southern Sweden, shows that body mass index, or BMI for short, tended to decrease with increasing AMY1 copy numbers in subjects with a low starch intake, and tended to increase with increasing AMY1 copy numbers in subjects with a high starch intake.
The lowest average BMI and body fat percentage was seen in participants with a low AMY1 copy number and a high dietary intake of starch.
In other words, individuals with a high starch intake but low genetic capacity to digest starch had the lowest risk of obesity. That’s the opposite of what the cracker test predicts.
To quote the research team directly:
“Individuals with high starch intake but low genetic capacity to digest starch had the lowest BMI, potentially because larger amounts of undigested starch are transported through the gastrointestinal tract, contributing to fewer calories extracted from ingested starch.”
Your “sweet spot” for carbs – the level of carb intake that allows you to lose fat, but still gives you the energy to train hard, and where you don’t feel like you’re living like a monk and can’t eat anything that tastes nice ever again – does vary from person to person.
However, putting a cracker in your mouth and timing how long it takes to change in taste is highly unlikely to tell you where that sweet spot is.
The numbers for what your daily carb intake should be appear to have been plucked out of the air, and the whole thing strikes me as a marketing gimmick that gave Moalem something to talk about when he appeared on the Dr Oz show. A gimmick that van Tulleken and the BBC appear to have swallowed hook, line and sinker.
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