What Are Macronutrients

What Are Macronutrients? - Definition, Functions & Examples

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Macronutrients are energy-providing chemical substances consumed by organisms in large quantities. The three macronutrients in nutrition are carbohydrates, lipids, and proteins.

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DefinitionNutrients are environmental substances used for energy, growth, and bodily functions by organisms. Depending on the nutrient, these substances are needed in small amounts or larger amounts. Those that are needed in large amounts are called macronutrients.

There are three macronutrients required by humans: carbohydrates (sugar), lipids (fats), and proteins. Each of these macronutrients provides energy in the form of calories. For example:

Carbohydrates: 4 calories per gram Proteins: 4 calories per gram Lipids: 9 calories per gram

This means that if you look at a food label and it lists 10 gramsof carbohydrates, 0 grams of protein, and 0 grams of fat, that food would contain 40 calories.

CarbohydratesHumans need carbohydrates in the largest amounts. Currently, the USDA recommends that adults get 45-65% of their daily caloric intake from carbohydrates. Carbohydrates are incredibly importantto the diet because:

Carbohydrates are easily metabolized (chemically broken down) and used as the body's main fuel source.

All of our bodily tissues have the ability to use the simplecarbohydrate glucose as energy. When the body uses carbohydrates for energy, it can use other macronutrients for other jobs, like tissue growth and repair.

The brain, kidneys, muscles and heart all need carbohydratesto function properly.

Carbohydrates aid in the synthesis of certain amino acids. Fats can only be properly metabolized when carbohydrates are

present. Indigestible carbohydrates, in the form of fiber, are

necessary for intestinal health.

Carbohydrates are primarily found in starchy foods (like grain and potatoes), fruits, milk, and yogurt. Other foods like vegetables, beans, nuts, seeds, and cottage cheese contain carbohydrates, but in lesser amounts. Carbohydrates can be simpleor complex, which refers to their chemical structure. Simple carbohydrates taste very sweet (like fruit sugar), while complex complex carbohydrates taste savory (like starch in potatoes).

Fiber is an indigestible form of carbohydrate. Since humans cannot break down these carbohydrates, they pass through the digestive system whole and take other waste products with them. Diets low in fiber have problems with waste elimination, constipation, and hemorrhoids. Diets high in fiber have shown decreased risk for obesity, high cholesterol, and heart disease. Fruits, vegetables, and whole grain products all contain high amounts of fiber.

Proteins

Currently the USDA recommends 10% - 35% of calories in the human diet come from protein. The typical American diet contains more protein than is strictly necessary. Proteins are important in thediet because:

Protein is the major constituent of most cells, making up more than 50% of the dry weight.

Proteins define what an organism is, what it looks like, andhow it behaves, because the body is made of thousands of proteins.

Proteins are used to produce new tissues for growth and tissue repair, and regulate and maintain body functions.

Enzymes, used for digestion, protection, and immunity, are made of protein.

Essential hormones used for body regulation require protein. Proteins may be used as a source of energy when

carbohydrates are not available.

Protein is found in meats, poultry, fish, meat substitutes, cheese, milk, nuts, legumes, and in smaller quantities in starchyfoods and vegetables. People who consume a vegetarian diet can get plenty of protein if they keep a balanced diet.

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AbstractThe digestion and absorption of macronutrients (carbohydrates, lipids, proteins) and micronutrients (vitamins and minerals), essential for the requirements of the human body, take place mostly in the small intestine. In most cases digestion occurs both in the gastrointestinal lumen and at the mucosal surface, continuing in some cases within the enterocytes themselves. Substrate-specific enzyme processes exist for polysaccharide carbohydrates and polypeptides, linked with digest-specific active co-transporters to aid absorption at the cellular level. The hydrophobicity of fats makes lipid handling more complex, requiring the creation of intraluminal emulsions and micelles which present lipid degradation products to the enterocytes. The intestine (small bowel and colon) has additional mechanisms for absorption and re-absorption of water and key electrolytes. In most cases micro-nutrients are liberated from dietary macromolecules by non-specific digestion and then absorbed passively (or as other lipid-soluble moieties in the case of the fat-soluble vitamins) but some specific transporters are also involved as in the case of vitamin B12. Quantitatively minor but important digestion and nutrient absorption also occur in the colon.Type:

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References

Vitamin, Macronutrient and Micronutrient DeficiencyMicronutrients refer to trace minerals and vitamins required in minute quantities, as opposed to macronutrients, required in larger amounts (fats, carbohydrates, proteins, calcium, phosphate and magnesium etc). Inadequate oral intake of dietary vitamins and micronutrients is prevalent in patients with CD [Rigaud et al. 1994; Pons et al. 2009; Gerasimidis, 2011].Factors that contribute to decreased food intake, independently of disease activity, include loss of appetite, hunger and depressed mood [Rigaud et al. 1994]. An analysis of the 7-day dietary pattern of 74 patients with CD showed failure to meet recommended daily dietary intake of all nutrients, except vitamin B12, despite adequate protein/energyintake and a normal body mass index. This was particularly so with intake of vitamins A, C and E, folate, calcium and zinc, with prevalence rates of each deficiency exceeding 40%. These findings were independent of disease activity, although the study was not powered to assess this as a primary outcome [Aghdassi et al. 2007].

Consequences of micronutrient deficiencies range from overt clinical syndromes, including anaemia (due to deficiencies in iron, B12 and folate), osteomalacia (vitamin D), peripheral neuropathy (vitamin E), night blindness (vitamin A), beriberi (thiamine) and stomatitis or glossitis (vitamin B groups). In many cases, however, patients with micronutrient deficiencies present with nonspecific symptoms such as fatigue and depression.

Iron deficiency anaemia is the most common 'extra-intestinal' manifestation of inflammatory bowel disease (IBD), with prevalence rates ranging from 36% to 88% [Gisbert and Gomollon, 2008; Gerasimidis, 2011]. In a study evaluating the practice of iron replacement in patients with IBD in Europe, only 18–30% of 1173 patients with CD with iron deficiency anaemia received iron intravenously [Stein et al. 2011], whereasinternational guidelines [Gasche et al. 2007] advocate that the intravenous, rather than oral, may be the preferred route of iron administration. However, a prospective multicentre trial of 100 patients with CD or ulcerative colitis (UC) with iron deficiency demonstrated an improvement in iron levels and quality of life regardless of the route of administration [Gisbert et al. 2009]. Of the 78 patients with a haemoglobin between 10 and 12 g/dl (women) or between 10 and 13 g/dl (men)treated with oral iron, only 5% developed intolerance, necessitating a switch to the parenteral route. An explanationfor the strikingly high rate of tolerance of oral iron in thisstudy may be the relatively low dose used (equating to approximately 100 mg elemental iron). Indeed, when choosing the dose of oral iron to administer, it is important to recognize that a maximum amount of 10–20 mg can be absorbed from the gastrointestinal tract (proximal small bowel) [Rimon et al. 2005].

Vitamin B12 deficiency occurs in approximately one-fifth of patients with CD [Yakut et al. 2010; Headstrom et al. 2008], although this will clearly be higher in patients with loss of

absorptive terminal ileal surface due to disease activity or after surgical resection. Although deficiency is thought to occur in all patients after resection of more than 60 cm of terminal ileum [Mowat et al. 2011], a small study of 42 patientswith resections of between 20 and 60 cm demonstrated abnormal B12 absorption in 52%, highlighting the need to monitor these patients carefully [Duerksen et al. 2006]. Recent British Society of Gastroenterology guidelines suggest giving B12 replacement in all patients with ileal resections greater than20 cm and yearly B12 measurements if less than 20 cm [Mowat et al. 2011].

Low serum and red cell folate levels have been reported in up to 28% of patients, particularly in those with active disease [Elsbourg and Larsen, 1979; Hoffbrand et al. 1968], though more recent studies using modern laboratory techniques put this much lower at 4.3% [Oldenburg et al. 2000]. In addition to poor intake and malabsorption, folate deficiency can also result from competitive inhibition from sulphasalazine use. There is a concern that folate deficiency may be associated with colorectal cancer in patients with UC or colonic CD, possibly secondary hyperhomocysteinaemia, which leads to DNA methylation and DNA instability [Phelip et al. 2008]. Observational studies suggest that folate supplementation may be associated with reduced colorectal neoplasia in IBD [Lashner et al. 1997], and the recently published British Society of Gastroenterology guidelines [Cairns et al. 2010] notethat folate supplementation may be beneficial, especially in patients who may have folate deficiency due to sulphasalazine therapy, although these guidelines acknowledge that data supporting this statement are relatively sparse.

Malabsorption rather than dietary insufficiency is the likely main underlying mechanism leading to fat-soluble vitamin deficiencies [Kuwabara et al. 2009] which, in turn, can be associated with metabolic bone disorders [Kuwabara et al. 2009].Vitamin D deficiency can, of course, result in osteomalacia.

Studies of bone mineral density in patients with CD demonstrate variable rates of osteopaenia and osteoporosis, due to the definitions used, but all show significant reduction in bone health with osteopaenia rates of 23–77% [Abitbol et al. 1995; Bjarnason et al. 1997; Pigot et al. 1992] andosteoporosis rates of 17–30.6% [Bjarnason et al. 1997; Compston et al. 1987]. As stated, vitamin deficiencies, including vitaminK, are associated with reduced bone density, and other risk factors in IBD include corticosteroid use [Dear et al. 2001], jejunal involvement or bowel resection [Robinson et al. 1998], stricturing or penetrating disease [Cravo et al. 2010], and ongoing inflammation [Paganelli et al. 2007]. Vertebral fractures (often asymptomatic) have been demonstrated in 20–22% of patients with CD, including those under 30 years old [Klaus et al. 2002]. The exact pathogenesis is unclear but interesting data from 26 patients with CD in remission suggestsuppressed bone formation with normal bone resorption, which may provide therapeutic avenues in the future [Schoon et al. 2001].

Depletion of vitamin A stores can occur in patients with CD inthe absence of any clinical manifestations of this vitamin deficiency, such as night blindness [Bousvaros et al. 1998]. As vitamin A is stored entirely in the liver, serum vitamin A is a poor marker of body reserves [Rumi et al. 2000], thus making detection of deficiency difficult. Patients with primary sclerosing cholangitis are particularly at risk of deficiencies in vitamin A and other fat-soluble vitamins due to chronic cholestasis [Jorgensen et al. 1995]. However, deficiency of vitamin E leading to peripheral neuropathy is a rare clinical occurrence [Bousvaros et al. 1998].

What Are Macronutrients

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