By Michael and Emily
Some of our latest work, published in the journal Nutrients, provides new insights into how fructose in the diet of a nursing mother can be passed on to her baby through breastmilk. And this secondhand fructose, though small in quantity, can increase risk for obesity in the developing baby.
Interestingly, newborns are not well-adapted to handle fructose – it is not a natural component of breast milk, baby’s ideal first food. But given the increase in fructose in our food supply, largely thanks to processed foods and drinks that contain high fructose corn syrup, we were curious to see if fructose was detectable in breast milk of nursing moms as well. And if so, we wanted to know if this secondhand fructose exposure could contribute to obesity in their babies.
Fructose is often thought of in connection with fruit, so it may sound healthy. The quantity of fructose in a piece of fruit is not of concern; in whole fruit the fructose comes along with beneficial vitamins, minerals, and fiber which helps the fructose to be released into the blood supply slowly over time. But when consumed in excess in processed, sweet food and drinks, it is harmful to the body. This is not just because there is more fructose, but also because especially when delivered through a drink, it surges quickly into the blood stream. Unlike other types of sugar, fructose is processed almost entirely by the liver and when consumed rapidly and in excess is converted to fat in the liver. When fat builds up in the liver it can become very harmful. Other studies have shown that fructose is particularly damaging to children during critical periods of growth and development. But now we are starting to discover how fructose can affect infants as well.
To answer our questions about fructose, breast milk and risk for obesity, we worked with colleagues at the University of Oklahoma on a small proof of concept study. We collected breast milk from 25 mothers and tested it for various sugars, and we weighed and measured their babies’ body composition at one and six months of age. These breastfed infants consumed less than 8 ounces of formula a week and had no solid foods, according to their mothers.
We found that fructose could be detected in the mothers’ milk and it was associated with higher body weight and body fat in the infants. Although the levels of fructose were extremely low, a single microgram of fructose per milliliter of breast milk was associated with a 5 to 10 percent higher body weight and body fat for infants at six months of age. This is a tiny amount of fructose – about the same weight as a single grain of rice. Other studies have shown that even tiny amounts of fructose can re-program fat cells to be more likely to grow faster.
The main sugar and source of carbohydrates and energy in breast milk is lactose. Lactose is made by joining a glucose sugar to a galactose sugar (unlike sucrose or regular table sugar which is composed of a glucose connected to a fructose). However, this study shows us that a mother’s milk can contain trace amounts of fructose as well. This likely depends on how much fructose is in a mother’s own diet. Breast milk is the best source of food and nutrition for a baby. But this study shows us that new moms should consider how much fructose they consume themselves in order to prevent passing it along to their babies. With this new study, we are now beginning to believe that any amount of fructose in breast milk is risky.
It can be a challenge to eat well as a breastfeeding mom. New moms are especially hungry —they need about an extra 500 calories a day to support milk production. They are also often tired, which can lead to cravings for sweets. We are not advocating taking out all sugar, but there are a few key tips that we suggest for moms to keep the amount of sugar they eat within moderation and to especially avoid fructose:
- Avoid products made with high-fructose corn syrup or with any added fructose
- Replace sugar-sweetened beverages, including fruit juices, with water or herbal tea
- Focus on eating whole foods rather than food products (which often contain sugars)
- Reserve sweet bakery items, flavoured yogurts, and other sweetened foods for special treats rather than everyday staples
Michael Goran, Ashley Martin, Tanya Alderete, Hideji Fujiwara, David Fields. Fructose in Breast Milk Is Positively Associated with Infant Body Composition at 6 Months of Age. Nutrients, 2017; 9 (2): 146 DOI: 10.3390/nu9020146