metabolism

Metabolism

The sum of all chemical reactions within a cell

Four main metabolic pathways

Biosynthetic, fuel storage, oxidative processes, waste disposal

Anabolic processes

Synthesize larger molecules from smaller components

Catabolic processes

Break down larger molecules into smaller components, releasing energy

Dietary components

Fuels, essential amino acids, essential fatty acids, vitamins, minerals, water, xenobiotics

Healthy BMI range

18.5 – 24.9 kg/m²

BMR (Basal Metabolic Rate)

Energy needed to stay alive at rest

Factors lowering BMR

Age, sex, dieting/starvation, hypothyroidism, decreased muscle mass

Factors raising BMR

Higher body weight, hyperthyroidism, low ambient temperature, fever/infection

Overnight fast

Decreased insulin, glycogenolysis, liver glycogen provides glucose (~80g)

Gluconeogenesis

Making glucose from non-carb sources (lactate, amino acids, glycerol)

Starvation >4 days

Liver produces ketones, brain adapts to ketones, BMR falls

Malnutrition

Deficiency, excess, or imbalance of energy or nutrients causing adverse effects

Vitamin functions

Co-factors in metabolism, gene expression, structural components, antioxidants

Vitamin C (Ascorbic acid)

Collagen synthesis, antioxidant, improves iron absorption

Vitamin B12 (Cobalamin)

DNA synthesis, protein synthesis, energy production

Daily protein requirement

0.8g/kg/day

Excess fat storage

As triglycerides in adipose tissue (~15% water, ~15kg total)

Excess carb storage

As glycogen in liver (up to 200g) and muscle (150g)

Excess protein storage

As muscle mass (~80% water, ~6kg total)

Prudent Diet

5+ fruit/veg servings, limit free sugars, saturated fat, sodium, alcohol

Protein requirement in Prudent Diet

0.8 g/kg/day

Saturated fat limit

≤30g/day men, ≤20g/day women

Sodium limit

≤2.4g/day (6g salt)

Alcohol limit

≤14 units/week over ≥3 days

What is metabolism?

The sum of all chemical reactions that take place within each cell.

What are the four main pathways through which dietary components are metabolized?

Biosynthetic, fuel storage, oxidative processes, waste disposal.

What is the difference between anabolic and catabolic processes?

Anabolic processes synthesize larger molecules from smaller components; catabolic processes break down larger molecules into smaller components.

What type of process synthesizes larger molecules from smaller components?

Anabolic.

What type of process breaks down larger molecules into smaller components?

Catabolic.

Which metabolic process provides energy via the ATP cycle?

Catabolism.

What are the seven main categories of dietary components?

Fuels, essential amino acids, essential fatty acids, vitamins, minerals, water, xenobiotics.

What are essential amino acids?

Amino acids that cannot be synthesized by the body and must be obtained from the diet.

What are essential fatty acids?

Fatty acids that cannot be synthesized by the body and must be obtained from the diet.

What are xenobiotics in the context of diet?

Foreign chemical substances not naturally found in the body, often from diet or environment.

What percentage of protein by weight is nitrogen?

Approximately 16%.

What is the molecular formula of glucose?

C₆H₁₂O₆.

What is the molecular formula of fructose?

C₆H₁₂O₆.

What is the molecular formula of galactose?

C₆H₁₂O₆.

What is sucrose composed of?

A disaccharide composed of glucose and fructose; formula C₁₂H₂₂O₁₁.

What is lactose composed of?

A disaccharide composed of glucose and galactose; formula C₁₂H₂₂O₁₁.

What are triacylglycerols?

Three fatty acids esterified to one glycerol molecule; main form of stored fat.

What does "saturated" mean in reference to fatty acids?

All carbon atoms are fully bonded with hydrogen atoms, no double bonds.

What does it mean that lipids are "more reduced" than other energy sources?

They have more C–H bonds, allowing more energy release upon oxidation.

What is the healthy BMI range?

18.5 – 24.9 kg/m².

What does DEE stand for?

Daily Energy Expenditure.

According to 2020 England data, what percentage of men were overweight or obese?

67%.

According to 2020 England data, what percentage of women were overweight or obese?

60%.

According to 2020 England data, what percentage of men were obese?

26%.

According to 2020 England data, what percentage of women were obese?

29%.

What happens to excess dietary fuel?

It is stored as fat (adipose tissue), glycogen (liver and muscle), or muscle protein.

How is excess dietary fat stored?

As triglycerides in adipose tissue (about 15% water, ~15 kg total).

How is excess dietary carbohydrate stored?

As glycogen in liver (up to 200 g) and muscle (~150 g).

How is excess dietary protein stored?

As muscle mass (~80% water, ~6 kg total).

What percentage of water is in adipose tissue?

About 15%.

What percentage of water is in muscle tissue?

About 80%.

What is BMR?

Basal Metabolic Rate – the energy needed to stay alive at rest.

What energy uses are included in BMR?

Respiration, cardiac contraction, biosynthetic processes, tissue repair, maintaining ion gradients.

List the conditions required for measuring BMR.

Post-absorptive (12-hour fast), lying still at rest, thermo-neutral environment (27–29°C), no stimulants in last 12 hours, no heavy exercise in last 24 hours, steady state (30 mins).

What factors lower BMR/RMR?

Age, sex (typically lower in females), dieting/starvation, hypothyroidism, decreased muscle mass.

What factors raise BMR/RMR?

Higher body weight/BMI, hyperthyroidism, low ambient temperature, fever/infection/chronic disease.

What equations are used to calculate BMR?

Harris Benedict (2019), Schofield (1985), Henry (2005).

What is a rough estimate for BMR?

1 kcal/kg body mass/hour.

What daily energy intake does NICE (2006) recommend for non-severely ill adults?

25–35 kcal/kg/day.

Give an example calculation using the Henry equation for a 70 kg person.

(70 kg × 16) + 545 = 1665 kcal/day.

What happens during an overnight fast?

Insulin secretion decreases, glycogenolysis occurs, liver glycogen provides glucose.

How much glucose does the brain require daily?

About 150 g/day.

How much glycogen does the liver have after an overnight fast?

About 80 g.

What is gluconeogenesis?

The production of glucose from non-carbohydrate sources.

What substrates are used in gluconeogenesis?

Lactate, amino acids (from muscle, intestine, skin), glycerol (from fat breakdown).

What hormone increases during gluconeogenesis?

Cortisol.

What happens in starvation longer than 4 days?

Liver produces ketones from fatty acids, brain adapts to using ketones, BMR falls.

What process breaks down fat during starvation?

Lipolysis.

What process breaks down protein during starvation?

Proteolysis.

Define malnutrition.

A state of nutrition with a deficiency, excess, or imbalance of energy, protein, or other nutrients, causing measurable adverse effects.

What are the adverse effects of malnutrition?

Effects on tissue/body shape/size/composition, body function, and clinical outcome.

List the roles of vitamins in the body.

Co-factors in metabolism, gene expression, structural components, antioxidants.

What is Vitamin C also known as?

Ascorbic acid.

What are sources of Vitamin C?

Fruit and vegetables.

Is Vitamin C heat stable?

No, it is heat labile.

What are the functions of Vitamin C?

Collagen synthesis, improves iron absorption, antioxidant.

What is Vitamin B12 also known as?

Cobalamin.

What are the functions of Vitamin B12?

Protein synthesis, DNA synthesis, regenerates folate, fatty acid synthesis, energy production.

List all the B vitamins.

Thiamin (B1), Riboflavin (B2), Niacin (B3), Pantothenic acid, Vitamin B6, Biotin, Folate, Cobalamin (B12).

What is Vitamin A also known as?

Retinol.

What is Vitamin D also known as?

Calciferol.

What is Vitamin E also known as?

Tocopherol.

What is Vitamin K also known as?

Phylloquinone, Menaphthone.

What is the daily protein requirement?

0.8 g/kg/day.

What is the Prudent Diet?

A balanced diet guideline promoting health.

How many servings of fruit/vegetables are recommended daily?

5+ servings.

What should meals be based around?

Starchy carbohydrates.

What percentage of energy should come from free sugars?

No more than 5%.

What is the daily protein recommendation in the Prudent Diet?

0.8 g/kg/day.

What is the saturated fat limit for men per day?

No more than 30 g.