Many of us do not digest lactose, the sugar in cow’s milk, after the age of 3 years. This is the norm in the human species. How to know if a person is intolerant to lactose?
According to scientists, about half of people complaining of chronic diarrhea would be intolerant to lactose, the dominant sugar of cow’s milk1. But where does this famous lactose intolerance come from? All babies tolerate lactose: we are equipped with an enzyme, called lactase, which helps digest the sugar lactose in the milk. Around the age of three to six years, in human species, this enzyme is not or poorly expressed and we cannot digest lactose properly. Hence troubles when consuming dairy products in childhood and adolescence because this undigested lactose is causing toxins. This is the norm for humanity: 70 to 75% of the earth’s population cannot digest lactose after the age of three years.
But a minority of the inhabitants of the planet, those who go down as pastoralist peoples have a genetic mutation that allows them to continue to express lactase, even after the age of 3 years. Those people therefore can drink milk without experiencing disorders due to the absence of lactase. In Europe, those people are mainly the residents of the north. Further south, more intolerance is widespread. Lactose intolerance concerns more than 60% of the inhabitants of the south of France and 90% in Sicily.
Symptoms of lactose intolerance
Lactose is found in liquid milk, but also in yoghurts and cheeses. Normally, yoghurts contain no or little lactose because it is “digested” by the probiotic bacteria. But industrialists, to improve the creaminess of yoghurt and to erase their acidity often add milk powder, containing lactose. There is also lactose in many processed foods such as cold cuts and even medicines.
Cardiff University researchers have identified the symptoms of lactose intolerance in 133 patients for 48 hours after they had received 50 g of lactose, the equivalent of what is in a liter of milk2.
Aside digestive symptoms, here’s what they found: 100% of patients had the following symptoms: abdominal pain, abdominal distension, rumbling, flatulence. 70% of them had diarrhea (30% being constipated), 78% of patients complained of nausea and vomiting.
Aside systemic symptoms, here’s what the researchers also found: 86% of patients complained of headache and dizziness, 82% loss of concentration, impaired short-term memory, 71% of them suffered muscle aches, pains, stiffness and joint swelling, 40% of allergies, 24% cardiac arrhythmia, 30% of ulcers …
If you think you are lactose intolerant, you can have confirmation by DNA testing, or more commonly by a test that measures expired (total?) hydrogen after ingestion of 50 g of lactose (1 g / kg with children).
Who is affected by lactose intolerance?
According to experimental studies conducted on this subject, some of those who express more lactase can drink small amounts of lactose (about 10 to 12 g per day or the equivalent of a glass of milk) without suffering from specific disorders3. However the acceptability of lactose threshold varies from person to person: some tolerate a glass of milk, others are indisposed with a few grams of chocolate milk.
In the USA, the National Institute of Diabetes and Digestive and Kidney Diseases estimates that 30 and 50 million people suffer from lactose intolerance4. In France, no official estimates have been made, but 41% of adults have problems digesting milk or … 20 million. Yet lactose spreads a bit more every year in our food …
- Campbell AK, Waud JP, Matthews SB The molecular basis of lactose intolerance. Sci Prog. 2005;88(Pt 3):157-202.
- Matthews SB, Waud JP, Roberts AG, Campbell AK Systemic lactose intolerance: a new perspective on an old problem. BMJGlobal Health March 2005 Vol. 81 – 953
- Sklar M, Wasserman B What is Lactose Intolerance? Physicians Committee for Responsible Medicine
- Sibley E, Fisher R, Pennington J, McDowell MA Lactose Intolerance National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)