Food Science
The Science Behind Food and Nutrition
Food science explores the complex chemistry, biology, and physics of what we eat. Understanding these scientific principles can help us make better dietary choices and appreciate how our bodies use the foods we consume.
What Is a Calorie?
A calorie is technically a unit of energy—specifically, the amount of energy needed to raise the temperature of 1 gram of water by 1 degree Celsius. In nutrition science, we typically use kilocalories (kcal), though we commonly refer to them simply as "calories."
When scientists determine the calorie content of foods, they traditionally use a device called a bomb calorimeter, which measures the heat released when food is completely burned. However, the human body does not extract energy from food through combustion, but through a complex series of digestive and metabolic processes.
The Atwater System
The calorie values we use today are generally based on the Atwater system, which assigns standard energy values to each macronutrient:
- Carbohydrates: 4 calories per gram
- Proteins: 4 calories per gram
- Fats: 9 calories per gram
- Alcohol: 7 calories per gram
Biochemistry of Macronutrients
Carbohydrates: The Body's Preferred Energy Source
Carbohydrates are composed of carbon, hydrogen, and oxygen atoms arranged in chains of varying complexity. During digestion, they are broken down into their simplest form—glucose—which provides immediate energy for cellular functions.
Scientific Insight:
The brain alone requires about 120 grams of glucose per day, accounting for approximately 60% of the body's glucose utilization at rest. While the body can use alternative energy sources when carbohydrates are limited, glucose is the preferred fuel for optimal brain function.
Proteins: The Building Blocks
Proteins are complex molecules made up of amino acids linked by peptide bonds. The human body uses proteins primarily for structure (building cells and tissues) rather than energy, though they can be converted to glucose through a process called gluconeogenesis when carbohydrates are scarce.
The Thermic Effect:
Proteins have a high thermic effect of food (TEF)—meaning your body uses more energy to digest and process proteins compared to carbohydrates and fats. Approximately 20-30% of the calories in protein are used for digestion and processing, compared to 5-10% for carbohydrates and 0-3% for fats.
Fats: Concentrated Energy Storage
Fats (or lipids) are composed of fatty acids and glycerol. They provide the most concentrated form of energy at 9 calories per gram—more than twice that of proteins and carbohydrates. The body efficiently stores excess energy as fat tissue for future use.
Why Fats Have More Calories:
Fats have more hydrogen atoms relative to their carbon and oxygen content compared to carbohydrates. When metabolized, these additional hydrogen atoms create more energy-storing bonds, yielding more ATP (adenosine triphosphate, the energy currency of cells).
The Science of Metabolism
Metabolism encompasses all chemical reactions that occur in the body to maintain life. In terms of energy, metabolism consists of two primary processes:
1. Catabolism: Breaking Down for Energy
In catabolic reactions, complex molecules are broken down into simpler ones, releasing energy in the process. Digestion is a form of catabolism, as is cellular respiration, where glucose is converted to ATP, carbon dioxide, and water.
2. Anabolism: Building Up for Growth
Anabolic reactions require energy to build complex molecules from simpler ones. Examples include protein synthesis (building muscle) and fat storage (converting excess glucose to triglycerides).
Basal Metabolic Rate (BMR)
Your BMR represents the calories your body needs to maintain basic life functions at rest, accounting for 60-75% of your total daily energy expenditure. It's influenced by factors like:
- Body size and composition (more muscle increases BMR)
- Age (BMR typically decreases with age)
- Sex (men generally have higher BMRs than women)
- Genetic factors
- Hormonal health (especially thyroid function)
Food Chemistry: Why Cooking Changes Calories
Cooking does not just change the taste and texture of food—it alters its chemical structure, which can affect its calorie content and how efficiently our bodies can extract energy from it.
Gelatinization of Starches
When starches are heated in the presence of water, their molecular structure changes through a process called gelatinization. The tight crystalline structure of raw starch granules loosens, making them more accessible to digestive enzymes. This is why cooked starches (like rice or potatoes) are more easily digested and can provide more available calories than their raw counterparts.
Protein Denaturation
Heat causes proteins to unfold or "denature," changing their three-dimensional structure. This process makes the amino acids more accessible to digestive enzymes, potentially increasing the amount of protein your body can absorb. This is one reason why cooked eggs provide more bioavailable protein than raw eggs.
Resistant Starch Formation
Interestingly, when some cooked starches like pasta, rice, or potatoes are cooled after cooking, a portion of the starch recrystallizes into "resistant starch." This form of starch resists digestion in the small intestine and acts more like fiber, potentially reducing the calories your body can extract from these foods.
Calorie Availability: Not All Calories Are Absorbed Equally
The standard calorie values assigned to foods are averages that do not account for individual variations in digestion and absorption. Several factors affect how many calories your body actually extracts from food:
Food Structure
Whole or minimally processed foods often require more energy to digest and may have lower "net" calorie content. For example, a study found that whole almonds provided approximately 20% fewer absorbable calories than their nutritional label indicated because some fat remained trapped in the almond's fibrous structure.
Gut Microbiome
The population of bacteria in your intestines affects how many calories you extract from food, particularly from complex carbohydrates and fiber. Some gut bacteria break down otherwise indigestible fibers, producing short-chain fatty acids that provide additional calories.
Food Particle Size
Smaller food particles have more surface area exposed to digestive enzymes. This is why blended or well-chewed foods may provide more readily available calories than the same foods in larger pieces.
Applying Food Science to Healthy Eating
Understanding the science behind food can help you make more informed dietary choices. Here are some practical applications:
- Combine protein with carbohydrates to slow digestion and maintain steadier blood sugar levels
- Chill cooked pasta, potatoes, and rice before eating to increase resistant starch content, which may reduce calories and improve gut health
- Consider the thermic effect of food when planning meals—higher protein meals require more energy to digest
- Choose whole foods over processed ones when possible, as their complex structure may result in fewer absorbable calories
For more practical information on nutrition, explore our Nutrition Guide and Cooking Calories resources.
Playing Shredle regularly can help you develop an intuitive understanding of calorie content across different foods, making it easier to apply these scientific principles to your daily food choices.
Note: The information provided is for educational purposes only and is not intended as medical or nutritional advice. Consult with a healthcare professional for personalized dietary recommendations.