Macronutrient Breakdown: Carbohydrates, Sugars, and Fats

Understanding Macronutrients and DRIs

Macronutrients

Macronutrients, which include protein, carbohydrates, and fat, are required by the body in relatively large amounts (hence "macro"). All three provide energy. Fiber is a type of carbohydrate.

Dietary Reference Intakes (DRIs)

The Acceptable Macronutrient Distribution Ranges (AMDRs) are part of the DRIs. They recommend a balance of macronutrients, expressed as a percentage of total dietary energy, that is associated with:

• Maintenance of a healthy weight
• The lowest risk for chronic disease
• The lowest risk for nutrient deficiencies

Consuming macronutrients below or above these ranges increases the risk of chronic disease. Notably, the age group with the highest AMDR for fat is children aged 1-3 years.

A Closer Look at Sugars

Sugars are used to sweeten or preserve foods and provide functional attributes such as viscosity, browning, and texture.

Added Sugars

Added sugars are sugars and syrups added to foods during processing or preparation. They are not intrinsic to the food itself.

Total Sugars vs. Added Sugars

Total Sugars include all sugars naturally present in foods and beverages (like those in milk and fruits) as well as any added sugars. There is no Daily Value for total sugars because no official recommendation has been set for the total amount to consume daily.

Added Sugars include those added during processing (e.g., sucrose, dextrose), foods packed as sweeteners (e.g., table sugar), sugars from syrups and honey, and sugars from concentrated fruit or vegetable juices. The Daily Value for added sugars is 50 grams per day, based on a 2,000-calorie daily diet.

Americans get most of their added sugar from sugar-sweetened beverages, followed by sweet drinks and desserts like cookies and brownies. The average intake is 266 kcal/day, with a national average of 21 eight-ounce servings of sweetened beverages per week. Consumption is highest in Latin America.

Dietary Guidelines and School Lunch Programs

The 2020-2025 Dietary Guidelines for Americans (DGA) recommend limiting added sugar intake. Proposed changes to school lunches aim to reduce sugar and sodium, though flavored milk will remain. These changes involve a phased approach to limiting added sugars:

1. Limits on specific high-sugar products (cereals, yogurt, flavored milk).
2. Overall weekly limits on added sugars.

Final Rule on Added Sugars in Schools

Product-based limits are set to be implemented by the 2025-2026 school year:

• Breakfast cereals: No more than 6g of added sugars per dry ounce.
• Yogurt: No more than 12g of added sugars per 6 oz.
• Flavored milk: No more than 10g of added sugars per 8 fl oz.
• Competitive flavored milk (middle/high school): No more than 15g of added sugars per 12 fl oz.

Weekly dietary limits on added sugars are scheduled for implementation by the 2027-2028 school year.

Carbohydrate Requirements by Life Stage

The dietary requirement for carbohydrates is primarily driven by the needs of cells that rely on glucose, such as those in the brain, red blood cells (RBCs), white blood cells (WBCs), and the kidney medulla. The brain, in particular, uses glucose almost exclusively for energy. The criteria for determining the DRI for carbohydrates include:

• The average minimum amount of glucose utilized by the brain.
• Correlation with the estimated size of the brain from one year through adult life.
• The amount needed to prevent ketosis.

There is no Tolerable Upper Intake Level (UL) for carbohydrates, but there are recommendations to limit added sugars.

Recommended Intakes

• Infants (0-6 months): The brain uses 60% of total energy intake, and glucose turnover is four times that of adults. The Adequate Intake (AI) is 60 g/day (37% of calories).
• Infants (7-12 months): The AI is set at the median intake for this age group, which is 95 g/day (44g from human milk, 51g from complementary foods).
• Children and Adolescents (1-18 years): Based on adult data for brain glucose utilization. The Estimated Average Requirement (EAR) is 100 g/day, and the Recommended Dietary Allowance (RDA) is 130 g/day.
• Adults (19+ years): The DRIs are the same as for children. The EAR is 100 g/day, and the RDA is 130 g/day. Typical intakes are higher (Men: 200-330 g/day; Women: 180-230 g/day) to meet energy needs within the AMDR.
• Pregnancy: Needs increase due to a higher metabolic rate and fetal growth. The EAR is 135 g/day, and the RDA is 175 g/day.
• Lactation (Highest Requirement): Calorie needs are elevated for milk production. The EAR is 160 g/day, and the RDA is 210 g/day.

Low-Carbohydrate Diets and Metabolism

Low-carbohydrate diets require significant metabolic adjustment, leading to a state called ketosis. Long-term adherence to these diets may lead to:

• High cholesterol
• Increased risk of kidney stones
• Bone mineral loss

Metabolic Adaptation

While the optimal amount of dietary carbohydrate for health is unknown, humans can adapt to survive on fat and protein. This adaptation involves several metabolic adjustments:

• Increased lipolysis and release of non-esterified fatty acids (NEFA) from adipose tissue.
• Increased release of norepinephrine and epinephrine, which can stress the body.
• Increased conversion of NEFA to keto acids, which can provide up to 80% of the brain's energy needs.
• Breakdown of glucogenic amino acids to produce glucose.

Even during ketosis, the body still requires about 22-28 grams of glucose per day.

Comparing Keto and Paleo Diets

The Ketogenic (Keto) Diet

The Keto diet is a very low-carbohydrate, high-fat diet designed to induce ketosis. It was originally developed to treat epilepsy and is not intended for long-term weight loss.

• Pros: Can lead to short-term weight loss; eliminates refined grains and added sugars.
• Cons: Can be environmentally harmful, expensive, and may cause side effects like constipation, stomach upset, headache, fatigue, and dizziness. It restricts many fruits, vegetables, whole grains, milk, and yogurt.

The Paleo Diet

The Paleo diet is based on foods presumed to have been eaten during the Paleolithic era. It emphasizes lean meats, fish, fruits, vegetables, nuts, and seeds, while limiting foods that became common with farming, such as dairy, legumes, and grains.

• Pros: Can promote weight loss; is rich in vegetables; eliminates refined grains and processed added sugars.
• Cons: Excludes entire food groups like whole grains, legumes, and dairy; can be expensive and unsustainable.
• What to Eat: Fruits, vegetables, lean meats, grass-fed/wild game, fish, and healthy oils.
• What to Avoid: Salt, potatoes, legumes, dairy, refined sugar, and grains.

Understanding Dietary Fiber

• Dietary Fiber: Non-digestible carbohydrates and lignin that are intrinsic and intact in plants.
• Functional Fiber: Isolated, non-digestible carbohydrates that have beneficial physiological effects in humans.
• Total Fiber: The sum of dietary and functional fibers.