With the rapid development of the modern food industry, a large number of processed foods that heavily use refined carbohydrates and fats have emerged. These foods generally lack key components such as protein, fiber, and micronutrients, disrupting the satiety regulation system that humans developed over the course of evolution. As a result, the satiety signals provided by food are significantly mismatched with their energy content, forcing people to consume more calories to meet their basic nutritional and satiety needs. Since these processed foods are also more palatable, they further promote voluntary overeating. The 2025 World Obesity Report points out that obesity has become a global issue, and it is estimated that by 2030, over 2.9 billion adults worldwide will have a body mass index (BMI) above the normal range. The proportion of people with high BMI in China is rising and is expected to reach 5.1504 million by 2030.

A new concept, Satiety Per Calorie (SPC), rates foods based on the strength of the satiety signals they generate per unit of energy. Foods with high SPC values can help people naturally reduce calorie intake while staying full; in contrast, high-calorie-dense foods like fried foods and desserts are more likely to lead to unconscious overeating. A recent animal study published in Nature Metabolism indicates that neurons in the hippocampus record the sensory experience of high-calorie foods and can trigger strong eating desires even when not hungry, leading to overconsumption. Additionally, behaviors such as eating slower and reducing external distractions during meals can enhance the perception of satiety signals and lower the risk of overeating. Evidence from a review shows that slowing down eating can reduce calorie intake. Overall, the concept of SPC helps improve modern dietary structures and provides new ideas for controlling the prevalence of obesity. However, this concept still needs further experimental validation. This study will recruit 40 male volunteers with a BMI between 18.5-28 kg/m² and aged 18-44 years, to investigate the relationship between satiety per calorie and food intake.

This study plans to recruit 40 male volunteers in Shenzhen with a body mass index (BMI) between 18.5-28 kg/m² and aged 18-44 years. The recruitment criteria include being in good health without underlying diseases and conditions such as diabetes, infectious diseases, gastrointestinal disorders, hypoglycemia, cardiovascular or cerebrovascular diseases, mental illnesses, etc., not being allergic to common foods, and having no special dietary habits, eating disorders, irregular eating or lifestyle patterns, or smoking and drinking habits. Volunteer recruitment and screening will continue until the number of participants is sufficient, using standard methods such as posters and online resources. During recruitment, participants will be informed of the research plan and the potential risks to them. If they agree to participate, they will sign an informed consent form in accordance with the guidelines established by the Ethics Review Committee.

During participant recruitment for this study, we will ask potential volunteers to complete a questionnaire to screen for eligible participants based on the criteria mentioned above. The experiment starts at 9:00 in the morning and ends around 6:00 in the evening. The specific schedule is as follows: volunteers must fast and not have breakfast. At 9:00 a.m., they will arrive at the laboratory to measure blood glucose and have a self-assessment on the level of hunger. Then, body composition measurements will be conducted, including body composition analysis using TANITA, bone density scan using DXA, body composition assessment using BODPOD, and 3D scan. During the testing period, participants need to self-assess their hunger level every half hour. The specific test procedures and instrument models will be described in detail below.

At 11 a.m., volunteers will enter the metabolic chamber. Half an hour later, the measurement of resting energy expenditure will begin. At 12 p.m., five types of food will be provided to the volunteers for lunch, and the measurement of the thermic effect of food will begin at the same time. The food will be weighed and recorded both before being brought into the chamber and after the volunteers have finished eating. The grouping of volunteers will be described in detail below. From finishing lunch until leaving the chamber at 5 p.m., volunteers need to self-assess their hunger level every half hour. After that, volunteers will have dinner in the cafeteria, and the food for dinner will also be weighed and recorded before and after eating.

Body Composition Measurements:

The body composition of participants will be measured using a body composition analyzer (TANITA- MC980). This device provides separate weight readings for the right arm, left arm, body, right leg, and left leg. It can also measure complete body composition parameters, including body weight (BW), body fat percentage (fat%), fat mass (FM), BMI, and fat-free mass (FFM).

Bone density will be assessed via DXA (Horizon Wi, HOLOGIC). Participants will be asked to change into lightweight lab clothing, remove all metal accessories, and lie flat on the device as instructed. The device uses a low dose of X-rays to measure bone density and estimate body fat and muscle mass.

Body density will also be measured using the BODPOD (GS-X, COSMED), an air displacement-based device. Participants will be asked to wear a swimsuit and swim cap while seated in the device. This test provides an accurate measurement of body density and estimates body fat content based on density.

Height, waist circumference, hip circumference, and other measurements will be taken using a 3D scanner.

Volunteer Randomization:

Volunteers will be randomly divided into 5 groups, with 8 people in each group. Each group of volunteers will be provided with 5 types of food for lunch, determined according to the SPC values.

Group 1 (SPC 0-20) foods: cookies, French fries, cheese slices, donuts, and croissants, with the French fries purchased from McDonald's and the rest of the food purchased from a supermarket.

Group 2 (SPC 20-40) foods: pizza, burgers, rice, noodles, and hot dogs, with the burgers purchased from McDonald's and the rest from the supermarket.

Group 3 (SPC 40-60) foods: baked potatoes, baked sweet potatoes, apples, fried eggs, and oatmeal, all purchased from the supermarket.

Group 4 (SPC 60-80) foods: salad, carrots, silken tofu, pan-fried chicken, and boiled fish fillets, all purchased from the supermarket.

Group 5 (SPC 80-100) foods: boiled pumpkin, boiled broccoli, cucumbers, tomatoes, and lettuce, all purchased from the supermarket.

Foods that need to be boiled, fried, or baked will be prepared by someone who has cooking qualifications.

Inclusion Criteria:

• Body mass index (BMI) between 18.5 and 28 kg/m2
• Male
• 18-44 years old
• Healthy

Exclusion Criteria:

• No diabetes, infectious diseases, gastrointestinal disorders, hypoglycemia, cardiovascular or cerebrovascular diseases, mental illnesses, etc.
• Not being allergic to common foods.
• No special dietary habits, eating disorders, irregular eating or lifestyle patterns, or smoking and drinking habits.