Lactose, the principal carbohydrate in milk, is synthesised in a cow’s mammary glands. It is a disaccharide, composed of galactose and glucose. Lactose accounts for approximately 54% of the total non-fat solids of milk and contributes about 30% of the energy of full-cream milk. Cow’s milk contains about 4.63% lactose, which translates to 12 g lactose per 250 ml.
Lactose intolerance is the condition where a person does not have sufficient levels of lactase to digest lactose. Bacteria that occur naturally in the colon ferment undigested lactose received from the small intestine. This fermentation process may lead to the formation of acid and gas, while the body may simultaneously attempt to dilute the concentration of the lactose by re-absorbing water from the blood. This can cause vomiting and diarrhoea. Intakes of more than 12 g lactose (typically one glass of milk) may lead to symptoms such as abdominal pain, discomfort, bloatedness, wind, cramping and diarrhoea. Consuming small quantities of milk together with other foods and naturally fermented dairy products, such as yoghurt or maas, is recommended. Cheese contains virtually no lactose and should not have any adverse effect.
Milk contains the natural sugar, lactose (approximately 5 g per 100 ml). Generally sugar is not added to milk unless specified in the ingredients list e.g. in flavoured milks. The World Health Organisation (WHO) has focused on restricting added or free sugars, generally defined as ‘all monosaccharides and disaccharides added to foods by the manufacturer, cook or consumer, plus sugars naturally present in honey, syrups and unsweetened fruit juices’. The natural sugar present in milk (lactose) does not fall into this category, yet it must be declared as ‘sugar’ on the nutrition information label.
Before discussing how much lactose is present in milk, itis important to point out that according to law, all milk must have 3% protein/100 ml. The fat varies according to the prescribed fat classes. When the milk arrives at the dairy, all milk offered for human consumption is processed and the cream is skimmed to the legal limit through a process called ‘standardisation’ after which the milk is homogenised, heat treated and packed. During packaging, the percentage of fat is then added back.
The fat percentages in milk according to regulations are:
- > 3.3%—4.5% for full-cream
- > 1.5%-3.3% for medium-fat
- > 0.5%-1.5% for low-fat
- < 0.5% for fat-free.3
This means that the only potential variant is the carbohydrate (lactose) portion. Due to the slight change in volume of milk versus fat, there is a negligible increase in lactose in low-fat or fat-free milk versus full-cream milk. In other words, low-fat and fat-free milk by proportion have more ‘milk’ due to their lower fat content. If in doubt, a good place to look is on the list of ingredients. If there is no sugar on the ingredients list, it means that no sugar has been added to the milk.