You know that secondhand smoke is bad for your baby. You should also know about secondhand sugar. A new study, published in the journal Nutrients, finds that the sugar fructose can get into breast milk if a mother consumes too much of it in her diet. This is called feeding your baby “secondhand sugar.” [1,2]
Breastmilk is the best food for your baby. The American Academy of Pediatrics recommends exclusive breastfeeding for the first 6 months and continued breastfeeding, along with other foods, during your baby’s first year. Fructose is not normally found in breastmilk, and there is a good reason for that. Fructose increases your baby’s lifetime risk for obesity and diabetes. [1,2]
Healthy Breast Milk
Breastmilk is the best food for your baby because it provides a healthy balance of fats, proteins, sugars (carbohydrates), and nutrients. Studies show that breastfeeding reduces your baby’s risk for obesity, heart disease, diabetes, and asthma. Breastmilk has easily digested proteins, healthy fats, white blood cells that help fight infection, and carbohydrates that decrease unhealthy bacteria in your baby’s digestive tract. The main sugar in breast milk is lactose. 
What the Study Found
The study was done by researchers at the University of Southern California Medical School. The main findings were that fructose can pass from a mother’s diet into her breastmilk and that even tiny amounts of fructose significantly increased fat cells in babies at age 6 months. [1,2]
There were 25 women and babies in the study. All the babies were exclusively breastfed. The amount of fructose in breastmilk and the amount of fat in the baby bodies were recorded at age 1 and 6 months. The amount of fat – fat mass – was measured by a special type of x-ray called dual-energy X-ray absorptiometry. 
The researchers found that a one microgram increase of fructose in one milliliter of breast milk – 1,000 times less than the amount of lactose – was associated with a 5 to 10 percent increase in infant weight and body fat at age 6 months. [1,2]
What the Study Could Mean for You
This was one small study, but it strongly suggests that you should limit fructose in your diet if you are breastfeeding. The researchers caution that more studies are needed to confirm their findings. But fructose is not good for you anyway, so cutting back during breastfeeding makes good sense. [1,2]
In discussing their findings, the researchers suggest that fructose in an infant’s diet may “coach” a baby’s digestive system to store fat that become fat cells. Early exposure may set up a baby for a lifetime risk of obesity and all the diseases associated with obesity, like diabetes and heart disease. They recommend that mothers avoid added sugars and sweeteners during pregnancy and breastfeeding. [1,2]
Fructose is found in fruits and is used as a sweetener in many foods and drinks. A common sweetener is high fructose corn syrup (HFCS). Fructose is different from other sugars because it is sweeter and it is not well absorbed by the digestive system. It almost all goes to your liver, where it can become part of fat cells and fats that circulate through your blood as bad (LDL) cholesterol and triglycerides. 
Some common sources of fructose mentioned by the researchers of the study include high-energy drinks, frappuccinos, and fruit cocktails.  Common sources of fructose also include: 
- Soft drinks
- Agave nectar
- Processed sweets and deserts
Most fructose consumption in the United Sates comes from soft drinks.  Talk to your doctor about the amount and type of sugar in your diet. You might want to go easy on fruits high in fructose and avoid foods and beverages with added fructose.
Check your food labels for HFCS and for all added sugar. Food labels do not tell you they types of sugar they use. Fructose may appear as agave, corn sweetener, or honey. They do tell you grams of sugar per serving. Your best bet is to limit all added sugar. 
Do not forget about your child’s added sugar after breastfeeding and when foods are added to breastfeeding. Studies show that up to 50 percent of snacks, drinks, and desserts targeted at babies, toddlers, and children have at least one added sugar, HFCS is present in up to 4 percent of these products. 
According to the American Heart Association, women and children should limit added sugar to 25 grams per day (less than 6 teaspoons). Children under age 2 should not have any added sugar in their diet. 
- ScienceDaily, From mother to baby: Secondhand sugars can pass through breast milk.
- Nutrients, fructose in Breast Milk Is Positively Associated with Infant Body Composition at 6 Months of Age.
- American Pregnancy Association, What’s In Breast Milk?
- American Journal of Clinical Nutrition, How bad is fructose?
- American Heart Association, Children should eat less than 25 grams of sugar daily.