2020-03-07 New Zealand Listener

LISTENER MARCH 7 2020

THIS LIFE

G
ET

TY

IM

AG

ES

Mystery

in the milk

Research suggests A2 milk

is easier on the lactose-

intolerant, but more

investigation is needed.

The peptide beta-

casomorphin-7

in A1 milk may be

a contributor to

lactose intolerance.

Question:

You suggested (Nutrition, November 9) that A2 milk

could be helpful in controlling symptoms of lactose

intolerance. However, studies dating back to the 1960s

have repeatedly shown that children with lactose

intolerance have a deficiency of the enzyme lactase and

are unable to absorb lactose normally. This explains the

bowel symptoms of lactose intolerance, which include

discomfort, bloating and diarrhoea. Is it fair to say that

the role of A1 or A2 milk proteins in this process remains

unproven and largely speculative?

Answer:

S

ymptoms of lactose intolerance may

result from inflammation caused by

a protein found only in A1 milk. In

particular, scientists are beginning to

point the finger at a peptide, called

beta-casomorphin-7 (BCM-7), which is

produced from A1 milk during digestion

of beta-casein protein.

About 80% of the protein in cows’ milk is casein

and the remaining 20% is whey. Depending on the

genetic profile of the dairy cow, it may produce A1

beta-casein proteins in its milk, A2 beta-casein or a

combination of both.

New Zealand’s dairy herds have historically

produced A1-predominant milk. When we digest

A1 milk, BCM-7 is chopped off from the A1

beta-casein proteins and released. A2

beta-casein proteins differ slightly

in their construction and no

BCM-7 is produced.

So, BCM-7 is unique to

A1 milk digestion, and

therein potentially lies

the problem.

In 2017, Chinese

researchers conducted

a trial of A1 and A2 milk with 45

adults aged between 25 and 68.

All participants drank both milk

types, with a 14-day washout period

in-between. The researchers recorded

episodes of post-dairy discomfort

(PD3), along with cognitive

functioning, blood and faecal markers

and adverse events.

Drinking milk containing A1

beta-casein resulted in significantly

greater PD3 symptoms, higher

concentrations of inflammation-

related biomarkers, longer

gastrointestinal transit times, lower

levels of short-chain fatty acids

(indicating the health of our gut

microflora is being impaired) and

poor performance on cognitive tests.

What’s more, the worsening of PD3

symptoms after drinking A1 milk

occurred whether the participants

were lactose-intolerant or not.

Drinking milk containing only A2

beta-casein did not aggravate PD3

symptoms.

A

further clinical trial, published

in 2019 in the Journal of Pediatric

Gastroenterology and Nutrition,

involving 80 Chinese children aged

five or six, produced similar results.

Namely, that conventional milk

(containing both A1 and A2 beta-

casein) exacerbates the symptoms

of digestive discomfort associated

with lactose intolerance. It also

increased inflammatory and immune

biomarkers and cognitive test errors

compared with when A2 milk was

drunk.

However, in this second trial,

researchers noted that although all

the children drinking conventional

by Jennifer Bowden

NUTRITION