What are macronutrients, and what roles do they play in the body?
Nutritional needs are based on three major groups of macronutrients, for which the recommended intakes are defined by ANSES:
- Protein (0.8 to 1.0 g/kg/day for a sedentary adult, 1.6 to 2.2 g/kg/day for athletes or people over 65): a building block of muscles, enzymes, hormones, and antibodies. Maintaining muscle mass depends directly on the quality and quantity of protein consumed.
- Carbohydrates (40 to 55% of total energy intake): the primary fuel for cells, particularly those of the brain and red blood cells. Complex carbohydrates with a low glycemic index (legumes, whole grains, vegetables) are preferred for maintaining stable blood sugar levels.
- Fats (35–40% of total energy intake): precursors of steroid hormones, components of cell membranes, and carriers of fat-soluble vitamins (A, D, E, K). Essential fatty acids (omega-3 and omega-6) cannot be synthesized by the body.
What are the specific nutritional needs of older adults?
After age 65, nutritional needs change significantly:
- Increased protein intake (1.2 to 1.5 g/kg/day): to combat sarcopenia (age-related muscle loss). An intake of 2.5 to 3 g of leucine per serving is necessary to activate muscle protein synthesis.
- Vitamin D3: requirements increase (20 to 25 µg/day) due to reduced skin synthesis. A deficiency has been documented in 80% of people over 70 in France, with consequences for bone density and muscle strength.
- Calcium: Intestinal absorption decreases with age. Requirements remain at 1,000 to 1,200 mg/day.
- Vitamin B12: Absorption is reduced due to gastric atrophy in 30% of older adults. Regular monitoring of vitamin B12 status is recommended.
What nutritional needs are critical in a vegan diet?
A well-planned vegan diet can meet all nutritional needs, provided special attention is paid to certain nutrients:
- Vitamin B12: Absent from plant foods—systematic supplementation is essential. A deficiency leads to irreversible neuropathy if left uncorrected.
- Omega-3 DHA: found almost exclusively in fatty fish. Vegans can supplement with DHA derived from microalgae, the direct source of DHA in fish.
- Complete plant proteins: combine legumes (rich in lysine) and grains (rich in methionine) to obtain all essential amino acids. Aim for a slightly higher total intake (10 to 20%) to compensate for reduced digestibility.
- Iron, zinc, calcium, and iodine: reduced bioavailability in plant foods—soaking and sprouting improve absorption. Regular blood tests are recommended.
How should nutritional needs be adjusted for physical activity?
Physical activity significantly alters nutritional needs:
- Energy: Energy expenditure increases by 300 to 800 kcal/hour depending on intensity. Insufficient caloric intake inhibits adaptations to training and promotes muscle mass loss.
- Carbohydrates: A pre-competition carb load (8 to 12 g/kg/day) maximizes muscle glycogen stores.
- Protein (1.6 to 2.2 g/kg/day): distributed across 4 to 5 meals of 0.4 g/kg each to maximize post-workout anabolism.
- Post-workout blood glucose levels should be maintained by consuming carbohydrates within 30 to 60 minutes after exercise to stimulate anabolic insulin and replenish glycogen.
Is diet alone sufficient to meet nutritional needs?
For most healthy adults, a varied and balanced diet meets all nutritional needs. However, certain situations warrant targeted supplementation:
- Vitamin D3: Sun exposure is insufficient in France between October and April. Most scientific societies recommend a preventive supplement of 1,000 to 2,000 IU per day.
- Omega-3 DHA: Dietary intake falls short of recommendations for more than 80% of French people who do not eat fatty fish 2 to 3 times a week.
- Magnesium: Losses due to stress and sweating often exceed dietary intake. A supplemental intake of 200 to 400 mg per day is frequently recommended.
What role does hydration play in nutritional needs?
Water is the most vital nutrient: the body can survive for several weeks without food but only 3 days without water. Daily fluid requirements are 2 to 2.5 liters (food + beverages) for a sedentary adult under normal conditions, and increase with heat, physical exertion, and fever. Dehydration of just 1 to 2% of body weight reduces cognitive and physical performance by 10 to 20%, affecting concentration, short-term memory, and muscle strength.
