Several readers have emailed me to ask about babies’ ability to digest starch. Here’s one:
“I have noticed you recommending cereals for babies several times. I am sure that you are aware that many people look at feeding a baby grains before the age of one or even two as if you have offered your child strychnine. One of the reasons cited is that they supposedly do not have amylase to digest grains before that time. I have often wondered what exactly is happening to the cereal if it is not being digested, but the only statement I could find is something about it “rotting” in the gut.
I would love to get information from a scientific point of view on this topic. Everything I have been able to find thus far has been very biased towards one point of view or another. Either “cereal is the perfect first food. Easy to digest and enriched with iron” from the infant cereal companies or “Cereal is junk. No infant should ever eat grains. It is not natural or traditional and they can’t digest it” from online parenting sites.
I need a little clarity and common sense.”
I love the skepticism in Hope’s email, and I can also empathize with her frustration about how difficult it is to find good information about a seemingly simple question: Can babies digest starch? If you search for the answer to this question online, you will run into dire warnings of the dangers of giving starch to babies. But these sites might set off your woo detector – as they should. So, after receiving multiple emails about this question as well as seeing it mentioned in discussions on the Science of Mom Facebook page, I figured it was time to put some evidence-based information about babies and starch digestion on the Internet.
Researching this question has given me an excuse to read some classic nutrition physiology papers harkening back to the 1960’s and 1970’s, and it’s brought back memories of years in the lab, exploring nutrient digestion and metabolism. And starch digestion in infancy, it turns out, is a really neat story.
Let’s start with some basics about carbohydrate digestion.
What is starch? How is it digested?
Starch is a type of complex carbohydrate. Made from lots of glucose molecules bonded together in long, branching chains, it is a plant’s way of storing glucose – product of photosynthesis and source of energy – in a stable form. We find starch in grains, root vegetables, winter squashes, beans, and some fruits, like bananas. Starch is an important storage depot for the plant, and it also makes for tasty staple foods for cultures around the world.
Glucose is the major fuel for the cells of the body. When we eat starch, we have to break the bonds in those chains of glucose molecules, liberating them to be absorbed from the small intestine into our blood. Starch digestion begins in the mouth, where salivary amylase starts chopping up those large glucose chains. When this partially digested starch gets to the small intestine, amylase made and secreted by the pancreas jumps in to do more bond-breaking and is responsible for most of starch digestion in adults. A suite of enzymes produced by the cells lining the small intestine, including sucrase, isomaltase, maltase, and glucoamylase, work on the remaining short chains, finishing up the job and making glucose available for absorption.
Starch Digestion in Infants
Infants go through some incredible nutritional transitions in the first months of life. Prior to birth, their growth and development is fueled almost entirely by glucose from mom, absorbed across the placenta. After birth, they have to abruptly transition to an exclusive milk diet, which is high in fat and lactose, still a relatively simple sugar. As they start solid foods, babies have to adapt to a much more complex and varied diet. Around the world, starch is a major source of energy in the diets of children and adults alike. But when infants are first introduced to starchy foods – often in the form of cereals and porridges – starch is a novel nutrient to their digestive tract. They need to turn it into glucose, but are they equipped to do this?
It’s true that infants have low levels of pancreatic amylase, the workhorse of starch digestion in adults. Research in the 1960’s and 1970’s showed that pancreatic amylase activity, measured in samples of fluid from the small intestine, is almost non-existent in newborns. Activity starts to increase within the first six months, however, and continues ramping up throughout childhood. By four to six months, when many babies are introduced to starch in the form of cereals, there is some pancreatic amylase activity, but still much less than that found in older children and adults.
Looking at these results, scientists questioned whether babies could handle starch very well. But they didn’t throw up their hands and declare, “No starch for babies!” They kept asking questions and seeking answers. They must have been puzzled by the fact that babies appeared to digest starch just fine. For example, think of the experience of those who are deficient in another carbohydrate-digesting enzyme, lactase, which allows us to digest lactose, the carbohydrate in milk. What happens if they drink a glass of milk? They have obvious, uncomfortable symptoms of diarrhea, nausea, cramping, bloating, and gas. These symptoms weren’t apparent in young babies eating infant cereals, which in the U.S. in the 1970’s, were usually introduced to babies by 1-2 months of age. My mother-in-law recorded my husband’s first teaspoon of doctor-recommended rice cereal in his baby book at 4 weeks, yet her careful records didn’t include any concerns about a sudden onset of diarrhea.
And this approach to infant feeding wasn’t that unique to the U.S. Ethnographic reports are filled with examples of starchy first foods for young infants around the world: Millet flour at 3 months in Tanzania; corn porridge at 3 months in Zimbabwe; beans and rice at 4 months in Brazil; a little butter and flour at 3 days in Bhutan; rice mash at 3 weeks in Nepal; and prechewed taro root at 2 weeks in the Solomon Islands. If babies were eating starch this young, with no apparent clinical signs of malabsorption, there must be more to the story.
The studies of pancreatic amylase activity had only measured its activity in a test tube in the lab. Next, researchers took a more holistic approach and measured starch digestion in the babies themselves. A 1975 Italian study added starch from different sources (potato, tapioca, corn, wheat, and rice) to 1-3-month-old babies’ formulas and then checked to see what came out at the other end –- in the babies’ poop. It turned out that very little starch ended up in these babies’ diapers. When they were given between 1 tablespoon and ½ of a cup of starch per day, they appeared to digest more than 99% of it. The researchers then tried a larger dose, giving several 1-month-olds a full cup of rice starch. Three of these infants absorbed more than 99% of this amount. Two absorbed just 96%, the other 4% ending up in their diapers, along with some diarrhea. In other words, within the first few months of life, babies can digest small amounts of starch just fine, but give them too much and you’ll see some diarrhea. (And no, I’m not suggesting that we feed 1-month-olds cereal – this was just the research at the time.)
How is this digestion of starch possible if babies have so little pancreatic amylase at work?
There are probably several mechanisms at play:
1. Babies make lots of salivary amylase. Although newborns secrete little salivary amylase, production increases quickly in the first few months after birth [PDF], reaching near adult levels by 6 months of age. Salivary amylase appears to survive the acidic conditions of the stomach reasonably well and is protected by both the presence of starch and breast milk. Once it is dumped into the small intestine, where pH is more neutral, it resumes its work of breaking down starch.
2. Human breast milk has lots of amylase, 25x that found in raw cow’s milk. Interestingly, it is highest in colostrum, and decreases slowly during infancy, as salivary and pancreatic amylases are increasing. Like salivary amylase, breast milk amylase retains at least 50% of its activity even after several hours of exposure to the low pH of an infant’s stomach, passing into the small intestine ready to get to work. It also seems to be protected by proteins in breast milk. One researcher estimated that the amylase in 100 ml of breast milk was capable of digesting 20 grams of starch (equivalent to 2/3 cup of dry rice cereal) in one hour. This is one good reason to use breast milk to make up cereals for young babies, and studies show that amylase is stable in breast milk for hours even after repeated freezing and thawing.
3. Glucoamylase helps out in the small intestine. Glucoamylase is an enzyme made by the cells lining the walls of the small intestine. Like amylase, it breaks the bonds between glucose molecules in starch and shorter glucose chains. But unlike pancreatic amylase, glucoamylase is very active in infants, reaching adult levels as early as 1 month of age.
All of these sources of starch-digesting enzymes – salivary and breast milk amylase, as well as glucoamylase in the small intestine – appear to work together to help babies digest starch to glucose. But that isn’t the end of the story.
Studies have shown that a significant fraction of dietary starch isn’t digested in the small intestine of babies but passes on to the large intestine. Is this where it “rots” in the gut, as the alarmist blog posts claim? Not so fast. Bacteria in the colon ferment (quite a different process from rotting) these undigested carbohydrates as part of the healthy symbiotic relationship between our gut microbes and us humans. It happens in adults, too. Even with their full activity of pancreatic amylase, some starch escapes digestion in the small intestine, as does dietary fiber. These undigested foods help feed the microbes, who kindly benefit us in lots of ways. The end products of microbial fermentation in the colon are short chain fatty acids, which can improve nutrient absorption, enhance gut health, and even be used as a source of energy for both the microbes and the human host. Babies and toddlers may actually have faster colonic fermentation of starch than adults, which might represent an important pathway for them to fully capture the nutrients in their food. The addition of complex carbohydrates, including starch and fiber, to the diet of older babies and toddlers might help to develop those healthy microbes.
OK, so maybe babies can handle starch just fine. But is there any harm in waiting a year or two to introduce it, just in case?
I can think of a few reasons why we should be careful about limiting starch in a baby’s diet:
1. Waiting too long to introduce grains to your baby could end up increasing the risk of developing celiac disease, Type 1 diabetes, and wheat allergy. There seems to be a sweet spot kind of window in mid-infancy – probably between about 5 and 7 months, where introduction to a variety of foods, including grains, decreases baby’s risk of developing chronic disease and allergies later in life.
2. Eliminating starch can make it more difficult for babies to get the nutrients they need. Infant cereals are fortified with iron, one of the nutrients most likely to be limiting to infants, even in the developed world. They are stable for long-term storage, and it’s convenient to mix up just a tablespoon of cereal at a time. You can certainly meet the nutrient needs of babies without cereals, but it takes more work and experimentation. When Cee was a baby, she was not at all interested in eating fortified baby cereals, and I found other sources of iron for her. But if your baby likes cereals, I wouldn’t hesitate to include them as one of a variety of foods in his diet. Also, this concern about starch digestion and amylase tends to be focused on avoiding grains, but remember that legumes and many fruits and vegetables also have lots of starch. If you truly tried to avoid starch, you would really be limiting your baby’s opportunities to gain nutrients and experience with different tastes and textures.
3. There may be negative consequences to being anxious and restrictive about food with young children. We seem to have an ongoing obsession with restrictive diets. It used to be all about restricting fat, then all carbohydrates, and now grains are getting a bad rap. I don’t think this is healthy. Barring allergies or intolerances, eating a variety of foods from all the food groups pretty much ensures that you’ll meet your nutrient requirements without even trying. It allows you to relax and enjoy your food with the people you love, which is really what eating should be about. When you start eliminating food groups, you increase your risk of nutrient deficiencies, increase anxiety about food, and make it more difficult to share food. It’s one thing to make this choice as adults, but in my opinion, to impose it unnecessarily on our kids isn’t fair. When a two-year-old isn’t allowed to have a cupcake at a birthday party, he might feel different and deprived, and he’s lost a chance to practice eating treats in moderation. Parents of kids with food allergies have to work carefully to manage these situations, but for the rest of us, this kind of restriction is unnecessary.
The bottom line is that it is safe to feed babies starchy foods. They can digest them, and they are one part of a varied, balanced diet for babies that are ready to begin eating solid foods. I’ll be writing more about the transition to solid foods in the next few weeks.
What information did you get about introducing grains and other starchy foods to your baby? What did you actually do?