In both clinical and animal research, food intake is a key outcome measure used to assess how much food is consumed over a defined period. This measure is crucial in research on obesity, diabetes, malnutrition, and more. It is used in observational studies to explore eating behaviors — such as appetite, satiety, and hunger — and in randomized controlled trials to evaluate the efficacy of drugs and nutritional interventions. The term energy intake is similar but not identical to food intake. The following explanation highlights the differences between these related concepts:

What is food intake?

• Food intake generally refers to the quantity of food — measured in grams — consumed by a subject, whether human or animal.
• Food intake is measured in human studies using food diaries, surveys, or direct observation. In animal studies, food intake is precisely measured by weighing food before and after a set period. This approach is less common in human studies.
• Monitoring food intake helps assess eating behaviors and the efficacy of drug or diet interventions on consumption.

What is energy intake?

• Energy intake measures the amount of energy a person obtains from the food consumed.
• Energy intake is calculated based on the nutritional content of the ingested food (e.g., from fats, proteins, and carbohydrates) and is typically expressed in calories (kcal) or kilojoules (kJ).
• Two meals (or diets) with the same food weight can have very different caloric loads if one is richer in fats because fat has a higher caloric load per gram (9 kcal/gram) than carbohydrates and protein (both 4 kcal/gram). For example, if two meals, A and B, each weigh 80 grams but meal A contains 40 grams of fat, 20 grams of carbs, and 20 grams of protein while meal B contains 10 grams of fat, 35 grams of carbs, and 35 grams of protein, meal A will hold approximately 520 kcals of energy but meal B will hold 370 kcals. Therefore, if a person consumes the two meals, their food intake will be the same but their energy intake will be greater with the meal containing a higher fat content.
• While food intake tells us how much food is eaten, energy intake provides insight into the nutritional value of the food and its potential impact on metabolism.

Overall, both food intake and energy intake are essential measures in research. They provide scientists with a clear picture of dietary behaviors and the body's response to different interventions, aiding in developing effective strategies for conditions like obesity, diabetes, and malnutrition.