When energy expended equals energy consumed, weight remains stable.
Three main components influencing energy requirements:
Basal Metabolic Rate (BMR)
Thermogenic Effect of Food
Physical Activity Levels
Factors that Increase BMR:
Height
Growth
Body composition
Fever (body under stress)
Environmental temperature
Smoking
Caffeine
Certain hormones (premenstrual, thyroid)
Factors that Decrease BMR:
Aging (approximately 5% decrease per decade after age 30)
Starvation and Fasting
Lower levels of thyroid hormones
Satiety: Feeling of fullness and satisfaction after eating.
Proteins and fiber contribute to prolonged satiety.
Satiation: Communication with the brain to stop eating.
Stretch receptors in the stomach and hormones like cholecystokinin signal the brain.
Definition: Method to determine the amount of energy released from foods or by exercise.
Types:
Direct Calorimetry: Measures heat released from food or a person in a chamber. An increase in the temperature of surrounding water corresponds to the amount of heat being released.
Indirect Calorimetry: Measures the ratio of oxygen consumed to carbon dioxide expelled to estimate energy utilization.
Key objectives:
Describe the functions of water-soluble vitamins in the body.
Relate recommended intakes to food sources, bioavailability, and toxicity levels.
Identify requirements and upper levels of intake.
Describe deficiency symptoms and diseases related to water-soluble vitamins.
The content of vitamins and minerals can be quite heavy, so creating tables with functions, RDIs, and food sources is recommended for revision.
In the exam, specific RDIs don't need to be known by heart, but a general understanding of vitamin importance and food sources is important.
Vitamins are micronutrients that do not yield energy but are important for various functions.
Vitamins are organic (contain carbon), while minerals and water are inorganic (do not contain carbon).
Vitamins are chemically unrelated carbon-containing compounds found in living tissues.
Required in minute quantities for normal cellular function.
Essential for life events like reproduction, growth, and health.
13 vitamins are recognized as essential for humans.
Most vitamins must be derived from food.
Vitamin requirements vary according to life stage, from infancy to elderly.
Inadequate food intake can lead to vitamin deficiencies.
RDIs (Recommended Dietary Intakes) are generally higher than needed by most individuals and are regularly revised.
Australian RDIs are used.
RDI is the Estimated Average Requirement plus two standard deviations, meeting 97-98% of individuals' requirements.
RDIs have a buffer margin and likely exceed actual needs.
Requirements can vary depending on infection, illness, physiological stress, environmental factors, and lifestyle.
Some drugs can interfere with vitamin metabolism.
Misconception: More vitamins equal better health.
After a certain point, the body's absorption of vitamins plateaus, and excess is excreted via urine.
Some vitamins have upper intake levels; exceeding these levels can cause harm.
Watch the "Vitaminia" documentary to understand the implications of the supplement industry.
Studies show no benefit from vitamin supplements, and vitamin intake from food sources is generally better.
One study showed increased risk of death from cancer in people consuming lots of calcium supplements, but not from food. Supplements may have detrimental effects when over consumed.
Dietitians generally recommend supplements only when a true deficiency is confirmed through blood tests or when medical conditions impede vitamin metabolism (e.g., celiac disease, vegan diets leading to B12 deficiency).
Water-soluble vitamins (B group and C) are stored in peripheral tissues, and deficiency takes time to manifest.
Vitamin C deficiency takes 80-90 days to show.
Vitamin A deficiency takes 2-3 months.
Vitamin B12 deficiency takes 2-3 years.
Water-soluble vitamins are absorbed directly into the blood, circulate freely, and are excreted in the urine.
Fat-soluble vitamins (A, D, E, and K) are packaged into chylomicrons, absorbed into the lymph, and then into the blood.
Fat-soluble vitamins require protein carriers and are stored in cells associated with fat (e.g., liver).
Fat-soluble vitamins are less readily excreted and more likely to reach toxic levels when over consumed.
Vitamin E, C, and carotenoids: Antioxidant functions.
B vitamins: Coenzymes in metabolism reactions, TCA cycle.
Vitamin D and K: Bone health.
Vitamin A: Vision.
Vitamin K: Blood clotting.
Bioavailability: The amount of the vitamin consumed, absorbed, and the extent to which it is utilized.
`` rate and extent that a nutrient is absorbed and being used.
Vitamins can be destroyed by exposure to light, oxidation, cooking, and storage, particularly water-soluble vitamins.
Refrigerate fruits and vegetables.
Store fruits and vegetables in airtight wrappers.
Clean fruits and vegetables before cutting.
Microwave, steam, or simmer in small amounts of water.
Save cooking water for stews or casseroles.
Avoid long cooking times.
Vitamins are involved in many catalytic actions of enzymes in body cells.
B vitamins are part of the enzyme system that controls energy release from food.
Enzymes cannot work without specific vitamins in coenzyme form, something learned during energy metabolism discussions. See the textbook for a diagram of this process.
Coenzymes facilitate enzyme activity (they are not actually changed in the process).
Key water-soluble vitamins: B1, B2, B3, B5, B6, B12, Biotin, Folate, and Vitamin C.
For each vitamin, we will be looking at forms, functions, deficiency symptoms, toxicity outcomes, food sources, and nutrient reference values.
Today's focus: B1, B2, B3, and B5. The other vitamins will be covered the following week.