Carbohydrates
Carbohydrates provide glucose, an important nutrient for fetal growth and development. Carbohydrates are an important source of fuel during pregnancy and there is no need to restrict carbohydrate intake during a normal (non-diabetic) pregnancy.
The quality (type) of carbohydrate matters much more than the amount of carbohydrates. Complex carbohydrates provide a higher number of additional vitamins and minerals and are digested slower than simple carbohydrates for better blood sugar (glucose) stabilization.
Studies regarding a woman’s glucose levels during pregnancy indicate that a balanced approach is the best strategy. Pregnant women should aim for the most unprocessed, whole foods possible with every meal, but also with the understanding that favorite foods can be enjoyed as well, in moderation.
Women should not make any changes to their diet without talking to their health care provider (HCP), especially if they have diabetes, gestational diabetes, or are at risk for gestational diabetes. These women may require a different eating plan that can include carbohydrate restriction.
Background
Carbohydrates provide the body with glucose (energy), which is used to support all bodily functions and activities; it is also the preferred fuel for fetal growth and development.
Simple carbohydrates are digested and absorbed rapidly and provide fast energy boosts (i.e. long distance runners will eat glucose packets during runs) and are found in fruits, vegetables, milk products, sugar, honey, candy, and soft drinks.
Complex carbohydrates are digested much slower, but provide longer-lasting energy, and are found in whole grain breads, cereals, pasta, and rice, as well as beans, peas, and starchy vegetables such as potatoes and corn.
The best sources of carbohydrates are unprocessed or minimally processed foods which deliver vitamins, minerals, and fiber.
Other (less healthy) sources of carbohydrates include processed foods, especially those with added sugar (white bread, cookies, crackers).
Carbohydrates are found in a wide array of healthy and unhealthy foods; it’s not carbohydrates that are unhealthy, it’s the overall nutrient quality of the food that contains carbohydrates. An improvement in the quality of carbohydrates during pregnancy has enormous benefits, specifically for fetal growth and those at risk for gestational diabetes.
Pregnancy
The body digests food to produce sugar (glucose) that enters the bloodstream. In response, the pancreas produces insulin to move glucose from the bloodstream into the body's cells, where it's used as energy.
The pancreas produces even more insulin to make up for this resistance, which gets worse as pregnancy progresses. Some women’s bodies can adjust to these variations, but others cannot, therefore their blood sugar levels rise, and gestational diabetes develops.
Read Gestational Diabetes and Glucose Screening for more information.
Glycemic Index
The glycemic index (glycemia = the presence of glucose in the blood) is a system of assigning a number to carbohydrate-containing foods according to how each food increases blood sugar. The lower a food's glycemic index, the slower rise in blood sugar after eating that food. Therefore, the more processed a food is, the higher its GI score, and the more fiber or fat is in a food, the lower its GI score.
In general, the glycemic index is not as reliable as once thought and is falling out of favor. International organizations have advised against individuals using the index to determine healthy carbohydrate sources. This is mainly because individuals respond differently to certain types of carbohydrates, and solid, concrete values per food item may, therefore, be inaccurate and misleading.
Despite the above, a low-GI diet may be advantageous for those with gestational diabetes, as these types of foods overall may reduce the need for insulin and improve fetal health.
Women need to make sure they have a detailed discussion regarding their diet with their HCP if they have been diagnosed with diabetes, gestational diabetes, or may be at risk for gestational diabetes.
Fetal Growth
As stated above, the type of carbohydrate in the diet influences maternal and fetal glucose levels differently. Some carbohydrates have positive effects, while too much of other types have negative effects. Although the fetus does adapt well to sudden and drastic changes in carbohydrate intake, moderation is the best strategy.
Lower maternal blood glucose levels (carbohydrate restriction) can lead to reduced fetal growth and birth weight, but a high, continuous blood glucose level may lead to large for-gestational-age infants.
Consumption of healthy carbohydrates produces infants with birth weights between the 25th and the 50th percentile and often results in normal weight gain for the mother.
Restriction
Dramatic carbohydrate restriction is not advised in a normal pregnancy and can have negative effects on fetal brain development, glycogen levels, and neurotransmitter synthesis, even if the mother has plenty of energy and is eating enough protein.
Further, a strict, high protein-low-carbohydrate diet during pregnancy, when not specifically advised by an HCP, could cause intrauterine growth restriction and organ growth changes in the fetus, as well as increased cortisol (stress) levels, and an increased risk of hypertension, diabetes, and kidney problems in the mother.
Ketosis results when carbohydrate intake is restricted and the body turns to other energy sources, such as fat; ketone bodies are then released into the blood.
Ketone bodies freely pass through the placenta; a by-product of ketone bodies have been detected in fetal rat plasma after five-minutes of injecting the by-product into the mother’s blood.
Although not completely understood, ketone bodies may affect fetal growth and development, specifically the central nervous system.
These types of diets can also cause difficult short-term side effects (i.e. "keto flu") that could be exacerbated during pregnancy, such as: nausea, vomiting, leg cramps, loss of electrolytes, headache, fatigue, dizziness, insomnia, difficulty in exercise tolerance, and constipation.
Restriction may be necessary, however, in women with gestational diabetes. These women may need to count or limit their carbohydrate intake to 40% to 50% of their daily calories. Pregnant women should talk to their HCP before making any changes to their diet.
Food Sources
Pregnant women should choose whole grain, higher fiber, and low in added-sugar carbohydrate options whenever possible such as whole wheat pasta, whole wheat bread, oats, sweet potatoes, brown rice, nuts, seeds, beans, lentils, and fruits and vegetables (especially with their skins/peels).
Action
Women should not make any changes to their diet without talking to their HCP, especially if they have diabetes, gestational diabetes, or are at risk for gestational diabetes. These women may require a different eating plan or need to follow very specific recommendations.
During normal pregnancy, carbohydrate restriction is not recommended. The quality of carbohydrate is much more important than the amount; women should aim for complex carbohydrates whenever possible, and eat simple carbohydrates in moderation. Women can and should enjoy their favorite foods during pregnancy, keeping balance in mind.
Resources
Types of Carbohydrates (American Diabetes Association)
The Truth About Carbs (U.K. National Health Service)
Carbohydrates (American Heart Association)