Toxic Food: When Food Components Become Metabolic Poisons
One man’s meat is another man’s poison’ is a common quotation that is used in everyday life including in our feeding habits. The food that we eat contains various nutrients (carbohydrates, proteins, minerals, vitamins) which have to be digested and broken down into the various sub nutrients by the process of metabolism. This involves chemical and biological activities that take place at the cellular level. This breakdown of the nutrients utilizes energy and also produces energy for the body (Elsas 2011)
All humans need a full spectrum of nutrients. But in some people, some nutrients are genetically programmed to be inefficiently absorbed and as such, if consumed, will cause harmful effects in the body. This explains the concept behind ‘Inborn Errors of Metabolism’ whereby certain chemicals called enzymes in the body meant to metabolize nutrients are deficient or absent thereby causing its accumulation which results in harmful effects on the body.
In this situation, the nutrients that function as body builders and protectors become transformed into body destroyers.
Below, I will discuss in detail the inborn errors of metabolism and illustrate it with specific examples.
INBORN ERRORS OF METABOLISM
Harriet (2008) describes inborn errors of metabolism as genetic disorders that affect the metabolism of food. They are autosomal recessive traits that are not sex linked to any parent. They involve the deficiency or poor activity of enzymes that metabolize food resulting in medical problems and learning disorders. As described by Chau et al (1966, p. 15-10)
Protein Disorders: Amino acid, Organic, Urea cycle
Carbohydrate Disorders: Galactose, Fructose, Glycogen
Fatty acid disorders: Medium chain acyl-coA dehydrogenase deficiency, Long chain 3
Hydroxyacyl-CoA dehydrogenase deficiency.
The following are the various inborn errors of metabolism related to diet which have major harmful effects.
Glycogen storage disease type 1-4(glycogen digesting enzymes deficiency)
Galactosaemia (deficiency in galactose-1-P uridyltransferase)
Phenylketonuria (deficiency in phenylalanine hydroxylase)
Hereditary tyrosinaemia (deficiency in fumarylacetoacetate and fumaryl hydrolase)
Organic acidaemias: Methylmalonic acidaemia (deficiency in methylmalonyl CoA mutase)
Fatty Acids: deficiency of short-chain, medium-chain and long-chain acyl CoA dehydrogenases
Clinical features include:
Glycogen storage diseases: Lethargy, vomiting, hypoglycemia, hepatomegaly, hyperlipidemia, neutropenia, galactosaemia: Conjugated hyperbilirubinemia, diarrhea, hepatomegaly, failure to thrive.
Phenylketonuria: Aminoaciduria, jaundice, hepatomegaly, elevated liver enzymes.
Acyl CoA dehydrogenase deficiencies (Hale, Bennett 1992, p. 10): Hepatomegaly, muscle hypotonia, hyperuricemia, fasting hypoketotic hypoglycemia, Reye’s syndrome.
Others include congenital adrenal hyperplasia due to deficiency of 21- hydroxylase enzyme, Menke’s kinky hair syndrome due to deficiency in enzyme involved in zinc metabolism, and Wolman’s disease due to acid lipase deficiency.
The four common major inborn errors of metabolism will be discussed in detail below
- Galactosaemia. It is an enzyme deficiency leading to high levels of galactose in the blood. Galactose is a sugar found in milk. People with galactosaemia cannot eat dairy products in their die,t else they would suffer liver, kidney and brain damage (American Liver Foundation 2006). Dairy products include butter, milk, cheese, lactose, casein, whey, non-fat milk, lactalbumin etc. Dietary treatment: No milk or dairy products in diet.
- Phenylketonuria: is a deficiency of the enzyme that metabolizes phenylalanine, an amino acid. It has a 1:10000 incidence in the UK. Proteins like milk, eggs, meat, fish are not consumed in diet. Aspartame containing foods are also avoided. Elevated levels of phenylalanine can cause mental retardation, seizures, eczema and other behavior abnormalities. ( NIH 2000). Dietary treatment involves adherence to a strict low protein diet including special low or Nil - phenylalanine products and modified foods (March of dimes 2006).
- Maple Syrup Urine Disease: Individuals with this disease are not able to metabolize the branched chain amino acids:leucine, isoleucine and valine. Buildup of these amino acids can lead to neurological damage and death. Incidence is 1:200000. Infants typically present with musty urine odour.(Burton 1987)
Dietary treatment includes consumption of food with low in branched chain amino acids.
- Hereditary Fructose Intolerance: this is as a result of the deficiency of the enzyme that metabolizes the sugar fructose which causes extremely low blood sugar and liver damage. Fructose is typically found in fruit, honey and commercial sweeteners such as high-fructose corn syrup. Treatment is the complete elimination of fructose and sucrose from diet. (ADAM 2005).
In summary, inborn errors of metabolism are rare but collectively are common. They appear usually in infancy and continue till adulthood. Common foods that we think are acceptable in our digestive system are poisonous to others. Even some components of food like fructose are potent risk factors for chronic diseases like hypertension and diabetes mellitus (Flavin 2008). That is why it is essential for us to read the food labels before purchase of food items to avoid untoward body effects.