Exercise Benefits and Recommendations
Insulin resistance is decreased and blood glucose con-trol enhanced by regular aerobic exercise such as walk-ing, joggwalk-ing, bikwalk-ing, golfwalk-ing, hikwalk-ing, swimmwalk-ing, and moderate weight lifting. This appears to be the case as well in women with gestational diabetes. Weight lifting with the arms 3 days a week for 20 minutes per session for 6 weeks, and exercising on a recumbent bicycle at 50% VO2 max for 45 minutes three times a week, have been found to normalize blood glucose levels in some women.71
Levels of exercise that approximate 50–60% of VO2 max, or maximal oxygen uptake, are most often recom-mended for women with gestational diabetes. These levels are estimated in practice using a formula for heart rates associated with various levels of VO2 max. The formula is 220 2 age 3 0.50 (for 50% of VO2 max) 5 heartbeats per minute. In the case of a 29-year-old, the estimated heart rate at 50% of VO2 max would be 220 2 29 3 0.50, or 96 beats per minute. This would be the maximum heart rate she should experience while exercising. Levels of exercise should make women become slightly sweaty but not over-heated, dehydrated, or exhausted.71
deleterious effects of resulting ketonemia on fetal devel-opment, exclude this approach to blood glucose control.65 Correspondingly, restriction of pregnancy weight gain to below recommended amounts is not advised.71 Aggressive treatment of gestational diabetes that excessively limits caloric intake and weight gain increases the risk of SGA newborns.75 On the other hand, excessively high caloric balances and weight gains are of concern because they in-crease the risk of macrosomia.69
Type 2 diabetes in nonpregnant individuals is often treated with sulfonylurea oral medications. These drugs can-not be used in pregnancy because they cross the placenta and stimulate fetal insulin production. Other types of oral medi-cations such as glyburide and metformin are being tested for use among women with gestational diabetes.70 Oral agents that reduce blood glucose levels are not yet recommended for use in pregnancy due to the lack of randomized, control-led clinical trials that demonstrate their safety.65
Presentation of a Case Study
No two women with gestational diabetes share the same his-tory, risks, needs, and response to treatment. Case Study 5.2 represents an individual’s experience with the disorder.
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10-20% for breakfast
●
20-30% for lunch
●
30-40% for dinner
●
30% for snacks
● 65
Caloric levels and meal and snack plans are considered to be starting points and often require modifications after re-sults of blood glucose home monitoring tests are known.
Dietary management of gestational diabetes calls for control of carbohydrate intake because carbohydrates raise blood glucose values more than protein or fats do.
The following percent distributions of total calories from carbohydrate, protein, and fat have been established for gestational diabetes:
Carbohydrates: 40-50%
●
Carbohydrate calories should be obtained from complex carbohydrate foods that are high in fiber.
Protein: 20%
●
Fat: 30-40%
●
Fat calories should be obtained primarily from food sources of unsaturated fats. 65
The relatively low-carbohydrate, high-fat diet decreases the need for insulin by lowering the amount of glucose absorbed from food, and blunts postprandial increases in blood glucose and insulin levels. The addition of high-fiber foods to diet plans further enhances blood glucose control.
These changes in turn reduce fetal overgrowth and other adverse effects of insulin resistance and high blood levels of glucose during pregnancy.73
Low-Glycemic Index (GI) Foods
Whether low-GI foods benefit women with diabetes in pregnancy has been much debated and is somewhat con-troversial. Low-GI foods help women with gestational diabetes sustain modest improvements in blood glucose levels and decrease insulin requirements.74 Illustration 5.3 demonstrates this point by showing blood glucose levels after a meal containing white bread (GI = 70) or spaghetti (GI = 48) is consumed.
Nutritional Management of Women with Gestational Diabetes
A primary outcome goal for women with gestational dia-betes is well-controlled blood glucose levels. Other goals include the normalization of carbohydrate metabolism and a reduction in the mother’s and offspring’s subsequent risk of diabetes, hypertension, heart disease, and obesi-ty.65 For most women, diet and exercise changes will be the primary way to achieve these goals. In other women, supplemental insulin will be needed to help achieve glu-cose goals.
The following are components of the nutritional man-agement of women with gestational diabetes:
Assessing dietary habits and exercise habits
●
Developing an individualized diet and exercise plan
●
for blood glucose control
Monitoring weight gain, dietary intake
●
Interpreting blood glucose and urinary ketone results
●
Ensuring follow-up during pregnancy and
●
postpartum71
Women with type 2 diabetes coming into pregnancy are managed in much the same fashion as are women with gestational diabetes, only nutritional care begins earlier.
Ideally, normal blood glucose levels should be established prior to conception and then maintained in good control through pregnancy. Diet and exercise plans for women with type 2 diabetes can often be based on what has worked in the past, thus simplifying planning for needs associated with pregnancy.72
The Diet Plan In general, diets developed for women with gestational diabetes emphasize:
Whole-grain breads and cereals, vegetables, fruits,
●
and high-fiber foods
Limited intake of simple sugars and foods and
bev-●
erages that contain them
Low-GI foods, or high fiber carbohydrate foods
●
that do not greatly raise glucose levels Unsaturated fats
●
Three regular meals and snacks daily
● 72
Dietary planning is based around a calculated level of ca-loric need. These initial estimates of caca-loric need are intended to meet both maternal and fetal demand for energy while limiting increases in blood glucose levels. They are based on the pregnant woman’s weight status and weight gain goals for pregnancy. Estimated levels of caloric need according to women’s current weight status are shown in Table 5.10.
Women’s allotment of calories are generally spread across three meals and several snacks, including a bedtime snack to help prevent nighttime hypoglycemia. Propor-tions of daily calorie intake generally assigned to meals and snacks are:
Table 5.10 Estimating levels of caloric need in women with gestational diabetes65
Current Weight
Status BMI, kg/m2
Calories per kg Body Weight,
kcal/kg
Underweight ,18.5 up to 40
Normal weight 18.5–24.9 30 Overweight,
obese 25–34 25
Morbidly obese $34 20 or less
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Example Meal Plans Individualized diet plans for women with gestational diabetes include a variety of foods that correspond to the preferences and needs of women.
Two examples of such diet plans are shown in Table 5.11.
One menu provides approximately 2200 calories, the other 2400. Both menus include low-GI food sources of carbohydrate and meet nutrient needs of women during pregnancy.
Urinary Ketone Testing Women with gestational diabetes may be instructed to monitor urinary ketone levels using dipsticks. The presence of ketones indicates a negative calorie balance that is likely related to inad-equate calorie intake or skipped meals. A positive ketone urine test can be used to help women monitor and adjust calorie intake. When interpreting results of urinary ketone tests, keep in mind that 10–20% of pregnant women spill ketones after an overnight fast.71 This means the severity and consistency of positive findings for urinary ketones should be considered.
Postpartum Follow-Up
About 15% of women with gestational diabetes will re-main glucose intolerant postpartum, and 10–15% will de-velop type 2 diabetes within 2–5 years. Most women who managed their gestational diabetes with diet and exercise will not require monitoring of blood glucose levels after pregnancy. Women requiring insulin for glucose manage-ment should be tested for fasting and 2-hour postprandial blood glucose values before hospital discharge. A 75-gram oral glucose tolerance test is recommended between 6 to 12 weeks postpartum in women who were diagnosed with gestational diabetes during pregnancy but tested negative for glucose intolerance postpartum. Negative results should be followed by repeated glucose testing every 3 years.65
Prevention of Gestational Diabetes
Reducing overweight and obesity, increasing physical activity, and decreasing insulin resistance prior to preg-nancy are important components of reducing the risk of gestational diabetes.77 The risk of type 2 diabetes after pregnancy can be reduced substantially by healthful eat-ing, aerobic and resistance exercise, and maintenance of normal weight.65
Type 1 Diabetes During Pregnancy
Women with type 1 diabetes have deficient insulin output and must rely on insulin injections or an insulin pump to meet their need for insulin. Type 1 diabetes represents a potentially more hazardous condition to mother and fetus than do most cases of gestational diabetes.
Type 1 diabetes places women at risk of kidney dis-ease, hypertension, and other complications of preg-nancy.78 Newborns of women with this type of diabetes are at increased risk of mortality, of being SGA or LGA, and of experiencing hypoglycemia and other problems within 12 hours after birth. Hypoglycemia occurs in about half of macrosomic infants.58 Coming into pregnancy with this type of diabetes increases (by 2–3% to 6–9%) the risk of congenital malformations of the pelvis, central nervous system, and heart in offspring. Good control of blood glucose levels reduces the risk of malformations.
Maintenance of normal glucose levels from the start of pregnancy decreases the risk of fetal malformations and macrosomia substantially.79
Blood glucose control from the beginning of preg-nancy is also important because the fetal growth trajectory may be largely determined in the first half of pregnancy.
Exposure to high amounts of glucose and insulin when the fetal growth trajectory is being established may set the
“metabolic stage” for fetal accumulation of fat and lean tissue later in pregnancy.80 Even relatively low elevations in blood glucose levels can meaningfully increase birth weight.81 Unfortunately, only 10% of women with type 1 diabetes receive preconceptional care.80
Availability of a variety of new insulins, the insulin pump, and self-monitoring technology has revolutionized the care of type 1 diabetes during pregnancy.
Nutritional Management of Type 1 Diabetes in Pregnancy Primary goals for the nutritional man-agement of type 1 diabetes in pregnancy are continual control of blood glucose levels, nutritional adequacy of dietary intake, achievement of recommended amounts of weight gain, and a healthy mother and newborn.
Careful home monitoring of glucose levels and adjust-ments in dietary intake, exercise, and insulin dose based on the results are key events that increase the likelihood of reaching these goals. Monitoring urinary ketones is Time (min)
Incremental Glucose (mol/l)
6 5 4 3 2 1
00 60 90 120 150 180 210 240 300
Spaghetti Bread
*
a* *
* *
*
Illustration 5.3 Blood glucose response in people with type 2 diabetes to meals containing white bread or spaghetti.
source: G. Riccardi and A. A. Rivellese, “Diabetes: Nutrition in Prevention and Management.” Nutr Metab Cardiovasc Dis 1999; 9:33–6.
Reproduced with permission of Medikal Press S.r.l.
* denote statistical signifi cance.
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Copyright 2011 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part.