The Importance of Dietary Protein at Breakfast in Childhood

Leonidas Karagounis

Proteins (derived from the Greek word πρώτειος [proteios] meaning “first one” or “most important one”) are the major functional and structural components of all the cells of the body and participate in virtually all biological processes occurring in the body. Protein provides amino acids to the body that are used to build and maintain bones, muscles, and skin, and to produce molecules with important physiological roles, such as enzymes, hormones, neurotransmitters, and antibodies. To this end, dietary protein intake is imperative in child nutrition because, unlike adults, children are in a state of ongoing growth with nutrition and exercise being the most potent stimulators of physical growth and development [1–3]. To support normal growth and this activity-induced augmentation of lean mass, adequate dietary protein ingestion is important for providing the requisite substrates to support the remodeling and growth of these lean tissues, including muscles [1]. Skeletal muscle is the most abundant tissue in the body comprising 40–50% of body mass in humans and making up a large component of the overall lean tissue component. Beyond locomotion, skeletal muscle plays a key role in central metabolism and is responsible for about 60–70% of total glucose uptake and, therefore, directly impacting metabolic health [4]. Skeletal muscle as well as the whole body protein pool is highly metabolic and undergoes rapid diurnal turnover, a process that is intricately regulated by the balance between the rates of protein synthesis and degradation. The increase in whole body protein balance is an important adaptive response to both contractile activity (i.e., exercise) and nutrient availability (i.e., protein ingestion) [4]. 

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Fig. 1. Hypothetical diagram highlighting diurnal variations in whole body protein balance as a function of meal timing and amounts representative of Western eating behaviors.
In terms of nutrient availability, current research supports the concept of nutrient timing intake. For example, the diurnal turnover of whole body protein which in turn impacts whole body protein balance (Fig. 1) may to some extent be dictated by specific need states where macronutrient intake such as protein and carbohydrates may be imperative to support healthy physical growth and development. Specifically, similar to adults, a typically observed overnight fast in children (i.e., a ~10-h overnight fast) has recently been shown to result in a physiological state of increased catabolism as measured by increased rates of whole body protein breakdown. It is, thus, important that specific amounts of macronutrients be consumed at breakfast in order to attenuate such losses in whole body protein, which, therefore, provide an environment that supports healthy physical growth and development. The consumption of both carbohydrates and proteins seems to be important since both components contribute to the attenuation of whole body protein breakdown and the stimulation of whole body protein synthesis, which ultimately results in increased rates of whole body protein balance. Specifically, consuming as little as 7 g of milk protein as part of a CHO-containing breakfast seems to be sufficient to promote a positive net protein balance which persists up to 9 h following breakfast consumption when habitual diet and activity are controlled. Future research utilizing long-term studies is ultimately required to validate whether or not the benefits observed in the short term are translated into long-term benefits in terms of promoting increased lean tissue mass and, consequently, favorable body compositions in healthy active children.

References

  1. Rodriguez NR: Optimal quantity and composition of protein for growing children. J Am Coll Nutr 2005;24:150S–154S.
  2. Tobias JH, Steer CD, Mattocks CG, et al: Habitual levels of physical activity influence bone mass in 11-year-old children from the United Kingdom: findings from a large population-based cohort. J Bone Miner Res 2007;22:101–109.
  3. Baxter-Jones AD, Eisenmann JC, Mirwald RL, et al: The influence of physical activity on lean mass accrual during adolescence: a longitudinal analysis. J Appl Physiol 2008;105:734–741.
  4. Karagounis LG, Hawley JA: Skeletal muscle: increasing the size of the locomotor cell. Int J Biochem Cell Biol 2010;42:1376–1379.