The Impact of a High Protein Diet on Substrate Oxidation and Energy Metabolism

In the 19th century, researchers found out that the differences in the energy content of macronutrients (protein, carbohydrate and fat) can elicit different responses in the amount of calories individuals burn per day. It was demonstrated that protein has a metabolic advantage when compared to the other macronutrients (carbohydrate and fat). Since these findings, researchers all over the world started to study how diets differing in macronutrient distribution could result in different responses to energy metabolism. Diets with high amounts of protein (i.e. meats, eggs, dairy products, and grains) are becoming more popular, and studies have shown that when people eat high quantities of protein they lose weight and fat mass, maintain the weight loss, and burn more calories per day.

The investigators hypothesize that giving high amounts of protein to healthy women will increase the amount of calories and fat they burn per day, increase their satiety, and improve health markers when compared to a normal diet. The increased protein level will be achieved using a nutrition supplement consisted of soy protein, yogurt and honey.

To test this, the investigators plan to divide the participants in two groups: one will eat a normal diet and the other a diet with high amounts of protein during one and a half day. After one month they will change groups and eat the other diet for the same period of time. During this period consuming the diets (1.5 days), participants will stay inside a whole body calorimetry suite, which is similar to a hotel bedroom and is able to inform in the most precise way the amount of calories participants will burn and if they are burning more fat. Additionally, before and after each meal participants will have to answer a questionnaire about their appetite sensations and blood will also be collected to analyze health markers.

The aim of this study is to investigate the impact of a high protein diet (achieved through the use of a high protein supplement) versus standard diet on substrate oxidation and energy expenditure using a state-of-the-art live-in whole body calorimetry unit (WBCU).

This study will be an acute randomized, controlled, cross-over trial. Healthy women (n=24) will receive a run-in diet for three days and will then be randomly allocated into one of the following groups: 1) Control group receiving an eucaloric standard diet (55% of carbohydrate, 15% of protein, and 30% of lipid); 2) High-protein group: eucaloric high protein diet (35% of carbohydrate, 40% of protein, and 25% of fat) constructed around a soy protein-based meal replacement. The wash-out period will be of approximately one month. While receiving the diets in the WBCU for 32 hours, participants' overall change in energy metabolism including respiratory quotient will be assessed. Additional assessments include metabolic blood markers (glucose, insulin, lipid panel, peptide tyrosine-tyrosine, ghrelin, leptin, free glycerol, and free fatty acids), and appetite sensations (hunger and satiety). Body composition and energy requirements will be assessed at baseline using dual-energy X-ray absorptiometry and indirect calorimetry, respectively.

It is expected that the high-protein diet will increase lipid oxidation, and energy expenditure, with other favorable changes in the additional markers when compared to the control group.

Eligibility Criteria:
Inclusion Criteria:

* Healthy;
* Non-smoker;
* Female;
* Aged 18 to 34.9 years;
* Body mass index (BMI) between 18.5 and 24.9 kg/m² (preferably between 20 and 24.9 kg/m²);
* Regular menstrual cycle (lasting between 25 and 35 days).

Exclusion Criteria:

* Have previously been diagnosed with any kind of disease;
* Are taking any medications which may alter energy metabolism or body composition;
* Are lactose, gluten and/or soy allergic/intolerant;
* Follow a vegetarian, vegan or restrictive dietary pattern;
* Are pregnant or lactating;
* Have used nutritional supplements in the past two months;
* Perform over an hour per day of leisure time physical activity or more than seven hours per week of strenuous activity;
* Have had a nuclear medicine scan or injection of an X-ray dye in the past week;
* Have had a barium test/exam in the last two weeks;
* Claustrophobia.