Macronutrients
Chuong Pham-Huy, Bruno Pham Huy in Food and Lifestyle in Health and Disease, 2022
Macronutrients are nutrients that the body needs in large amounts for the production of energy for body activity. There are three classes of macronutrients: carbohydrates (sugars), proteins and lipids (fats). They can be metabolically processed into cellular energy. Water is also an essential nutrient required in a large amount, but unlike the other macronutrients, it does not yield energy. The energy from macronutrients comes from their chemical bonds (1). This chemical energy is converted into cellular energy that is then utilized to perform work, allowing our bodies to conduct their basic functions such as movement, respiration, excretion, growth and reproduction (1). A unit of measurement of food energy is the calorie. Both carbohydrates and proteins provide 4 kcal/gram, and lipids provide 9 kcal/gram for humans (3).
The obesity epidemic and weight loss surgery
Jenny Radcliffe in Cut Down to Size, 2013
We all get our energy from food and the energy content in food is measured in terms of food calories (kcal). Technically one calorie is the amount of energy required to raise the temperature of one kilogram of water by one degree Celsius. Food – fats, proteins, and carbohydrates and fibre – all release energy during respiration, the process by which nutrients are converted into useable energy in the body. Fats and alcohol generate the greatest amount of food energy, followed by proteins and most carbohydrates. Carbohydrates high in fibre are not so easily absorbed and contribute less food energy. The calorie count written on food packaging is calculated by estimating the constituent parts making up the product (protein, carbohydrate, fat and so on) and then converting this to an energy value using standardised tables.
Energy depletion
Shaun Phillips in Fatigue in Sport and Exercise, 2015
where H2O is water, ADP is adenosine diphosphate, Pi is inorganic phosphate, H+ is hydrogen, and ATPase is the enzyme adenosine triphosphatease. Only a small amount of ATP is stored in the body at any time (enough to fuel approximately 2 seconds of maximal intensity muscle contraction). Muscle energy turnover can increase 300-fold during explosive muscle contractions, so mechanisms of ATP replenishment are critical to maintenance of muscle performance. This is where food energy comes in. While food energy cannot be used to replenish ATP directly, it can do so through three primary metabolic pathways: the phosphocreatine (PCr) pathway, the anaerobic pathway, and the aerobic pathway. In the anaerobic pathway, glucose (from the blood or from glycogen stored in muscle) is metabolised to resynthesise ATP in a series of chemical reactions termed glycolysis. In the aerobic pathway, glucose and fatty acids are metabolised to replenish ATP in two enzymatic systems called the Krebs cycle and the electron transport chain. The PCr pathway does not used stored glucose or fat; instead, it metabolises a compound called PCr (Section 2.2.2). This compound is present in skeletal muscle and is not significantly influenced by normal dietary intake. The breakdown and resynthesis of ATP is a perpetual cycle, even at rest. Of course, during exercise when energy requirements are greater, ATP turnover is also greater. Therefore, logic dictates that the availability of food energy is critical to ensuring a sufficient supply of ATP for continued exercise performance.
The use of linear programming to determine whether breastfed infants can achieve a nutritionally adequate complementary feeding diet: a case study of 6–11-month-old infants from KwaMashu, KwaZulu-Natal, South Africa
Published in South African Journal of Clinical Nutrition, 2022
Nazeeia Sayed, Hettie C Schönfeldt
A 2019 Cochrane review25 on the value of animal-source foods for growth and development of infants found limited quality evidence and some uncertainty regarding the impact of animal-source foods when compared with cereal products or no intervention. Nevertheless, in this study, animal-source foods were an important contributor to nutrient intakes in infants’ diets in KwaMashu. An IFPRI report26 highlighted the fact that animal-source food energy derived from eggs and dairy products is relatively more expensive than food energy obtained from other animal-source foods, which may restrict their consumption. Consequently, these foods are most sensitive to prices impacting on their consumption.26 This IFPRI report also suggests that promoting household production of animal-source foods is likely to not have an impact on intakes, as these foods are valued for the high prices they can generate if they are sold. Research has been conducted on the addition of South African green leafy vegetables to maize meal, which showed that regular consumption could contribute to iron intakes.27
Putative Effect of Spirulina Extract on Enzyme Activities Participating in Lipid and Carbohydrate Digestion Processes
Published in Journal of Dietary Supplements, 2019
Reina Kishibuchi, Naoyoshi Nishibori, Takefumi Sagara, Kyoji Morita
In general, lipids and carbohydrates are highly nutritious and known to be major sources of food energy, thereby largely contributing to the fluctuations in energy balance. Therefore, the digestion and absorption of lipids and carbohydrates may be connected with the prevention and improvement of the energy balance disorder, and biologically active substances to suppress and delay their digestion and absorption can be considered to be effective and practically useful for preventing and improving the pathological conditions of metabolic syndrome (de la Garza, Milagro, Boque, Campio'n, & Marti'nez, 2011). For example, dietary fiber, which can delay the absorption of lipids and carbohydrates from the digestive tract, is commercially available and commonly used as a food supplement to suppress the postprandial elevation of blood glucose and triglyceride levels. On the other hand, lipase and α-glycosidase are enzymes in the epithelial cells of small intestinal mucosa that play key roles in the digestion and absorption of lipase and α-glycosidase. Substances to inhibit these enzymes are expected to reduce and delay the digestion and absorption of these nourishment, thereby being effective for the prevention and improvement of metabolic syndrome (Chiasson et al., 1998).
Assessment of Carbohydrate Availability, Fermentability, and Food Energy Value in Humans Using Measurements of Breath Hydrogen
Published in Journal of the American College of Nutrition, 2021
Their (1) “available energy” was undefined because we do not know the routes of energy loss from Promitor® fiber or what the energy is thought to be used for. Energy losses may be to fecal energy (FE), urinary energy (UE), gaseous energy (in methane in addition to hydrogen) (GaE), surface energy (SE) (in hair and skin, often considered minimal in food or ingredient energy studies in humans), and heat energy (HE). These energy losses together with the gross energy (GE) content of foods, components and ingredients, allows “available energy” to be defined as energy used for either metabolizable energy (ME) (3–5) or net energy for maintenance (inclusive of physical activity) (NEm) (6) or production (growth, etc.) (NEp) (6) or net metabolizable energy (NME). The last (NME) accounts for differences among protein, fat, available carbohydrate, and fermentable carbohydrate with which metaboloizable energy is used at a biochemical level (ATP and ATP equivalents) (5) and has been acknowledged to be a valid approach to derive food energy values (7) (8) should the NME system of food energy evaluation be adopted in food labelling or when used in research. Whatever definition applies, it is not determinable at present through measurements on breath hydrogen (see below).