2. Background

TB is a contagious disease related to poverty, undernutrition and poor immune function. TB morbidity and mortality are highest in developing countries. In 2012, there were an estimated 8.6 million new cases of TB (13% coinfected with HIV). There were 950 000 deaths due to TB among people who were HIV negative and another 320 000 among people who were HIV positive (7). While TB is more common among men than women, it is one of the top killers of women worldwide; including HIV-positive women, half a million women died from TB in 2012. There were an estimated 0.5 million TB cases and 74 000 TB deaths among children less than 15 years of age in 2012 (7).

More than 15 years of intensive effort to improve TB diagnosis, treatment and control have been successful in reducing TB prevalence and death rates. Between 1995 and 2012, 56 million TB patients were successfully treated in quality-assured national TB programmes, and over 20 million lives were saved through DOTS (Directly Observed Treatment – Short course) and the Stop TB Strategy (7). Still, the incidence of TB globally is declining only slowly and TB remains a major public health threat in most parts of the world (8).

Addressing comorbid conditions has value for improving access and response to TB treatment and it should be considered as part of the standard of care for people with TB. The aim of comprehensive care should be to improve general health and quality of life. The role of food and nutritional care is integral to successful health promotion and disease prevention. Undernutrition is both an important risk factor for, and a common consequence of, TB. It is therefore a common comorbid condition for people with active TB and is associated with increased risk of mortality and poor treatment outcomes (8–12). There is very limited evidence available to suggest that nutrition support, such as provision of supplemental or fortified food or specific nutrients, in addition to standard TB treatment, improves TB-specific treatment outcomes. However, nutrition assessment and care are critical components of improving rehabilitation and quality of life.

The integration of recommendations regarding nutrition care and support may include scaling up and strengthening nutrition care infrastructure, coordinating public health services and investing in capacity-building and training of health-care workers in the use of evidence-informed approaches to nutrition assessment and counselling. Opportunities exist to coordinate with other health programmes, such as HIV, childhood immunization and reproductive services.

Nutrition and tuberculosis

An essential dietary nutrient is a substance that a person needs to consume in order to live, grow and be healthy. Nutrients are required to regulate body processes and build and repair tissues and thereby promote health and prevent disease. Macronutrients (protein, carbohydrate and fat) are generally consumed in large amounts. Carbohydrate and some fat are converted to energy, while protein and some fat are used to make structural and functional components of human tissue. Micronutrients (vitamins and minerals) are consumed in small amounts and are essential for metabolic processes. Macronutrients and micronutrients work together to contribute to tissue regeneration and cellular integrity.

Malnutrition is a general term that refers to either overnutrition or undernutrition or both. Undernutrition refers to a state when the nutritional status of the person is suboptimal and thereby health and growth may be limited. Undernutrition may be due to illness that impairs nutrient intake and metabolism, or result from inadequate intake of macronutrients, micronutrients or both (10, 11, 13, 14).

Undernutrition is commonly associated with illness and infections such as gastrointestinal disorders and malabsorption, pneumonia, TB and HIV (15). Food insecurity can be a cause of malnutrition, as can alcohol misuse and illicit drug use (15), and a number of other conditions. In any case, both the underlying condition associated with undernutrition and the malnutrition itself warrant evaluation and treatment (15).

The association between TB and undernutrition has long been known. TB makes undernutrition worse and undernutrition weakens immunity, thereby increasing the likelihood that latent TB will develop into active disease (10). Most individuals with active TB are in a catabolic state and experience weight loss (9, 16, 17) and some show signs of vitamin and mineral deficiencies at diagnosis (18–21). Weight loss among those with TB can be caused by several factors, including reduced food intake due to loss of appetite,nausea and abdominal pain; nutrient losses from vomiting and diarrhoea (22, 23) and metabolic alterations caused by the disease. Low body mass index (BMI) (lower than 18.5 kg/m²) and lack of adequate weight gain with TB treatment are associated with an increased risk of death (9, 24) and TB relapse (25, 26) and can be an indication of severity of TB, poor treatment response and/or the presence of other comorbid conditions.

Macronutrient requirements in active TB

Active TB, like other infectious diseases, is likely to increase energy requirement, and data on the actual level of increase in energy requirements caused by HIV infection may be used as a guide. Studies show that subjects who receive food supplements during TB treatment tend to gain more weight compared with those not receiving food supplements, but the increase in weight gain has not been associated with improvement of TB treatment outcomes (17, 27).

There is currently no evidence to suggest that the proportion of dietary energy from macronutrients (e.g. protein, carbohydrate and fat), otherwise known as macronutrient distribution, is different for people with active TB than for those without TB. It is generally recommended that all people consume approximately 15–30% of energy as protein, 25–35% as fat and 45–65% as carbohydrate (28).

Micronutrient requirements in active TB

Low circulating concentrations of micronutrients, such as vitamins A, E and D, and the minerals iron, zinc and selenium have been reported from cohorts of patients beginning treatment for active TB (29–32). These usually return to normal after 2 months of appropriate TB treatment. Since studies have not been done on dietary intake near the time of diagnosis, it is unclear whether the low concentrations are related to low dietary intake, to metabolic processes or to the disease itself. It is unknown whether the observed return to normal concentrations is dependent on the quality of dietary intake.

Available guidance for treatment of malnutrition/undernutrition

BMI is the most commonly used indicator to measure the degree of thinness and fatness in adults over 18 years of age, while BMI-for-age-and-sex Z-score is used in children and adolescents aged 5–19 years (15). Weight-for-length or weight-for-height Z-score is the recommended indicator for children who are less than 5 years of age, with midupper arm circumference being used to identify cases in need of life-saving nutrition management.

Severe acute malnutrition

Severe acute malnutrition is a common cause of morbidity and mortality in many settings. Nutritional therapy aims to reduce the risk of death, shorten hospitalization and facilitate rehabilitation and a full recovery. Please see the World Health Organization (WHO) recommendations for definition and treatment of severe acute malnutrition in children, adolescents and adults (2–4).

Moderate undernutrition

In 2012, WHO published a technical note on Supplementary foods for the management of moderate acute malnutrition in infants and children 6–59 months of age (4). Currently WHO recognizes that the dietary management of moderate acute malnutrition in children should normally be based on the optimal use of locally available nutrient-dense foods. In situations of food shortage, or where some nutrients are not sufficiently available through local foods, specially formulated supplementary foods are usually required to supplement the regular diet; for those cases, the technical note provides orientation on the composition of supplementary foods.

The current recommendation for moderate undernutrition in adolescents and adults is to provide supplemental foods in the outpatient setting until BMI is normalized. The approach is that individuals with moderate undernutrition have different nutritional needs than either people without undernutrition or those with severe acute malnutrition. An individualized approach that addresses the various causes of moderate undernutrition is needed, since the appropriate therapy depends on the cause of undernutrition. For most people with active TB, assuming sufficient food is available, effective TB therapy will improve nutritional status by improving appetite and food intake, reducing energy/nutrient demands, and improving metabolic efficiency

Nutrition care or management of persons with active TB with moderate undernutrition, similarly to other persons with moderate malnutrition, includes assessing their nutritional status, identifying and treating the underlying causes of malnutrition and improving the nutrient intake through education, counselling, food assistance and other activities (2).

Social determinants of malnutrition and TB

Because undernutrition increases the risk of progression from TB infection to active TB disease, food insecurity and poor general nutritional status in the population are important contributors to the global burden of TB disease (8, 10, 11). Catastrophic health expenditure is a common consequence of TB diagnosis, treatment and care, which can lead to a worsening of food insecurity for TB patients and their families during the course of the disease. At least 75% of all TB cases are among people who are 15–54 years of age and in their prime working years (7). TB is a major cause of poverty aggravation because people with TB often face the double burden of reduced income and increased expenses: they are often too sick to work and their families have to pay expenses associated with treatment (33).

TB and pregnancy

Low birth weight, a predictor of infant morbidity and mortality, is more common in infants borne by women with TB (34–38). Infants of mothers with TB have increased risks of premature birth and perinatal death, while the mothers are more likely to have complications during pregnancy, with disorders of hypertension during pregnancy being the more common (35–37, 39, 40). Initiation of TB treatment earlier in the pregnancy is generally related to better maternal and infant outcomes (37, 39).

Adequate weight gain during pregnancy, which is associated with improved birth weight, is a concern in women with TB. In a study in Papua New Guinea, more than 80% of pregnant women with TB who did not receive TB treatment during pregnancy, or were treated for less than 4 weeks, lost weight or did not gain adequate weight during pregnancy. The majority of women receiving treatment for more than 4 weeks gained weight adequately; however, 38% did not gain adequate weight or lost weight in spite of longer TB treatment (39).

Pregnant women with TB have been noted to be at increased risk of developing preeclampsia (35, 40, 41). Health-care providers should be made aware of this risk and follow the WHO nutrition recommendations for women at risk of developing pre-eclampsia and eclampsia (6, 42). In populations where calcium intake is low, calcium supplementation as part of antenatal care is recommended for the prevention of pre-eclampsia among pregnant women, particularly among those at higher risk of hypertension.

Regardless of the presence of TB, the maternal requirement for micronutrients during pregnancy tends to be 25–50% higher, depending on the nutrient, than the prepregnancy requirements (43, 44). While there have not been any randomized controlled trials of micronutrient supplements in pregnant women with TB, multiple micronutrient supplements given during pregnancy in non-HIV infected populations have been effective in reducing rates of low birth weight, small-for-gestational-age infants, and anaemia (45–47). A Cochrane review of multiple micronutrient supplementation in HIV-infected women during pregnancy found that women who received the multiple micronutrient supplement including iron and folic acid had significantly better birth outcomes compared with those who received only iron and folic acid or no supplementation (48, 49). Infants of HIV-infected mothers given multiple micronutrient supplements had higher birth weights, and were less likely to have low birth weight, or to have been born severely pre-term or small-for-gestational-age (48, 49).

A healthy well-nourished woman should gain between 10 kg and 14 kg during pregnancy, to increase the likelihood of delivering a full-term infant weighing at least 3.3 kg (50). To support an average weekly weight gain of approximately 420 g and an average monthly gain of 1.7 kg in the second and third trimesters, a woman usually consumes 360 kcal/day (1.5 MJ/day) in the second trimester and 475 kcal/day (2.0 MJ/ day) in the third trimester, in addition to usual food (50). To support the additional protein requirements during pregnancy, women are advised to consume an additional 9 g/day of protein during the second trimester and 31 g/day in the third trimester. A pregnant adolescent needs 1.5 g protein/kg pregnant body weight to support her own needs as well as those of the fetus (51). Underweight pregnant women (BMI less than 19 kg/m²) can eat additional food, in order to achieve a total weight gain between 12.5 kg and 18 kg, with an average weekly weight gain of 510 g and an average monthly gain of 2 kg in the second and third trimesters (52).

TB and child household contacts

Owing to their proximity and frequency of contact, children with TB are usually infected by someone in their immediate household (53). When the positive case in the household is detected, screening for TB amongst household members is a means to detect TB early in children and other close contacts. Young children are particularly vulnerable, owing to their relatively immature immune systems (53). Undernourished children are at particular risk. Undernutrition and younger age individually increase the risk of household contacts of TB patients developing active TB disease (53, 54).

Child contact screening in many low- to middle-income countries may not be a priority, so children who are infected may be missed. An additional complication for screening household contacts for TB infection is the fact that children with mild to moderate malnutrition become anergic, meaning that they cannot mount an immunologic response to the TB skin test (14). This increases the likelihood of missing the TB diagnosis where skin testing is used. These children represent a potentially significant number of future TB cases (53, 55).

In the only nutrition intervention study identified in household contacts, family members of TB patients who received nutrition advice alone had almost six times the risk of developing active disease, compared with those who received a vitamin and mineral supplement with dietary advice (56). This study was conducted in New York City between 1941 and 1946, before the advent of TB chemotherapy. While intervention studies in child household contacts have not been conducted after the introduction of chemotherapy, improved nutrition among household contacts of TB patients, especially in children who are less than 10 years of age, might reduce the risk of contacts developing active disease.

¹ The definition of food assistance includes, in some cases, all interventions that address food insecurity and nutrition (including in-kind food aid, cash transfers and some forms of production and market support), while in other it is limited to direct food- and cash-based transfers.

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