Obesity prevention starts before birth

While it's critical to help the kids struggling now, it's just as important to consider those who are not yet born.

Risk factors for childhood obesity originate from the mother (before pregnancy) and extend into infant feeding (from birth to 2 years). These risk factors include: high maternal body mass index (BMI); gaining more weight during pregnancy than necessary; infants born smaller than usual (low birth weight), infants born larger than usual (high birth weight); infants not receiving breastmilk or lack of exclusive breastmilk; high protein intake (for infant).

Three hypotheses suggest why some children are at greater risk for obesity:

1. The fuel mediated in-utero hypothesis: If the fetus receives too much energy, like in the form of sugar, they experience metabolic changes which lead to obesity later. The mom may gain too much weight during pregnancy and birth a larger baby.

2. The accelerated postnatal weight gain hypothesis: Fast weight gain in infancy can lead to obesity and poor health outcomes, like cardiovascular disease. In particular, high protein diets during infancy have been reported to increase a child's risk of obesity. Interestingly, breastmilk has less protein than infant formula, and associations have been found between formula fed infants and later obesity.

3. The mismatch hypothesis: The fetus (before birth) is undernourished and the child (after birth) has access to copious amounts of unhealthy foods. If a fetus is undernourished, their body will best prepare for this type of environment – one without enough food. When the environment at birth is much different than during gestation (more food than the body expected), the child’s metabolism isn’t prepared for the high calorie foods and is at greater risk for obesity and other diseases.

Besides these hypotheses, the mother's health remains an important predictor of the health of the baby.

An under- or overweight mom is at risk of giving birth to either a small or large baby or a baby who could become stunted (not grow tall) – all which increase a child’s risk for overweight and obesity.

While it is commonly thought that pregnant women must "eat for two," that’s simply not the case. At best, expecting moms should increase their calorie intake about 10-15%. For example, if consuming 2,000 calories per day, that’s only an increase of 200-300 calories per day. An extra small meal or some extra snacks would suffice.

Weight gain targets should be personalized to the mom as her starting BMI changes the recommendation. For example, if an expectant mom is within the normal BMI range (18.5 – 22.9 for Asian ethnicity or 18.5 – 24.9 for other ethnicity), she should only gain 11.5-16 kg throughout her entire pregnancy, whereas an overweight expectant mom (BMI 23 – 24.9 for Asian ethnicity or 25 – 29.9 for other ethnicity) should gain 7-11.5 kg.

Further, weight gain only needs to occur from the second trimester, about 12 weeks after conception. It is best to have a "normal BMI" before becoming pregnancy, as higher BMIs can lead to health issues for the mom and baby.