Nutrient Profile and Muscle Protein Synthesis in Response to Corn Bread Made From Refined Versus Whole Grain Maize Flour

Indicators of longevity in humans include skeletal muscle mass and strength. Muscle mass is determined by the balance between myofibrillar protein synthesis and degradation, influenced by diet and physical activity. Muscle strength is closely tied to muscle mass, and activities like weight lifting until failure have been shown to increase muscle protein synthesis, enhancing muscle mass and strength over time. Protein intake is essential for maintaining a positive protein balance and promoting muscle growth. While animal proteins are generally more effective than plant proteins at promoting muscle protein synthesis, many cultures rely on staple plant-based foods, such as maize, rather than animal-based protein sources.

Maize (Zea mays) flour is a leading staple in African diets, where it is consumed in various forms, including porridges and breads like Ugali in East Africa or Fufu in West Africa. The nutritional profile of this corn bread varies greatly depending on whether it is made with refined or whole-grain maize flour. Whole-grain maize flour retains the bran, germ, and endosperm, providing higher fiber, vitamins, and minerals, while refined maize flour primarily contains the endosperm. Although refined maize is lower in fiber, it has a higher proportion of the leucine-rich zein, a major corn protein. These nutritional differences could significantly impact metabolism and overall health.

Given that approximately a fifth of the global population relies on corn meal as a dietary staple, understanding the impact of refined versus whole-grain maize flour on muscle protein synthesis and serum amino acid content could provide valuable insights for dietary guidelines and public health. This study aims to explore these effects, comparing the post-meal nutrient profile and muscle protein synthesis response to traditional African corn bread made with whole-grain versus refined maize flour.

The purpose of the study is to quantify and compare the serum nutrient and hormonal profile and muscle protein synthesis rates in response to consuming isonitrogenous servings of traditional African corn bread made from whole-grain or refined maize flour, paired with mung bean stew.

Specific aim 1: Describe the post-prandial nutrient and hormonal profile in serum in the 3 hours following consumption of a portion of mung bean stew with traditional African corn bread made with either whole grain maize flour or refined maize flour.

Specific aim 2: Compare the ability a portion of mung bean stew and traditional African corn bread made with either whole grain maize flour or refined maize flour to activate mTORC1-specific and whole muscle protein synthesis in an in vitro model of muscle.

Study participants will attend the CTSC Clinical Research Center on two separate occasions.

The two study visits will be scheduled over a 2-week period (i.e., once per week for 2 weeks) at the same time in the morning after an overnight fast of more than 12 hours. Participants will be asked to refrain from vigorous exercise, caffeine, nicotine, and alcohol for 24 hours before each visit. Female participants will schedule their visits within the first two weeks of their menstrual cycle to control for hormone fluctuations that may affect digestion and metabolism.

Upon arrival at the research center for the first test visit, each participant's height and weight will be measured. They will also complete a questionnaire covering their physical activity and dietary habits.

1. Baseline blood draw.

Participants will be seated in individual testing rooms equipped with reclining phlebotomy armchairs. A nurse will insert a 22G catheter into a forearm vein to collect an initial 5 mL baseline blood sample.

II. Test meal.

After baseline blood collection, participants will consume one of the two corn bread test meals. The meal consists of a serving of mung bean stew and an isonitrogenous amount of either whole-grain or refined maize flour-based corn bread:

The food will be weighed before cooking, and an eighth of a teaspoon of salt will be added to enhance palatability and participants will be asked to consume the meal within a 10-minute period, chewing thoroughly. Participants will also drink a 250 mL glass of water with the meal.

III. Postprandial blood draws.

After the test meal, participants will remain at the research site in their testing rooms for 3 hours, where they may bring books or electronic devices to occupy themselves. Five additional 5 mL blood samples will be collected at 30, 60, 90, 120, and 180 minutes post-meal, totaling 30 mL per visit, and 60 mL for participants completing the study.

Blood samples will be collected in 5 mL serum-separating tubes. Samples will clot before centrifugation at 1000 x g for 10 minutes. The serum will then be frozen and stored at -80°C. One milliliter from each serum sample will be used to determine nutrient and hormone concentrations. The remainder will be used for muscle protein synthesis and mTORC1 bioassay analysis.