A question was asked in the comment column under this article:
“Why Most People Cannot Tolerate
Drinking Milk” in this
link:
https://scientificlogic.blogspot.com/2023/
It reads:
“Very interesting explanation. My eldest brother who is 41 years old, 15
years older than me, can tolerate drinking milk, but not myself. He has been
drinking milk regularly since he was young without problem, but not myself. I
get severe diarrhea if I do. We are both from the same parents. So, there
should not be any genetic difference. Why then is this difference in tolerance
and health problems? Maybe you have the answer?
Sussie Chan”
……………………………………………………….
My answer to Sussie:
Thank you, Suzzie for your comment and question in my article “Why
Most People Cannot Tolerate Drinking Milk”?
Before answering your question, let
me explain just a little bit about genetics, and environmental influence on
genes. Just a bit will do together with other ‘irrelevant’ information if you
don’t mind so that we can understand nutrition better. Nutrition is far, far
more than just what food to take, what food to avoid or what foods are
health-protective, others disease causing.
The study of nutrition is a hectic
formal 4-year degree course involving almost the entire spectrum of biological,
biomedical sciences, chemistry, biochemistry, chemical analysis of
foods statistical analysis, sociology, agriculture and food production, soil science,
behavioural science, clinical medicine, especially in the diagnosis and recognition
of nutrition and nutrition-related diseases, These were subjects in our formal intensive
training during our postgraduate study at least at the University of London.
But I have little idea about other universities what they were taught there? The study of nutrition is done from bachelor’s
to master’s levels, onwards to doctoral and well past doctoral levels. So, what
I shall explain here is only a teeny-teeny tiny glimpse of it so that we can
answer your question better.
Although there is genetic
similarity between you and your brother, bear in mind genes do influence social
behaviour besides the types of proteins it expresses. Each cell expresses, or
turns on, only a fraction of its genes at any given time. The rest of the genes
are repressed or turned off. The process of turning genes on and off is known
as gene regulation. Gene regulation is an important part of normal development.
Genes are turned on and off in different patterns during development to make a
brain cell look and act different from a liver cell or a muscle cell, as
examples. Gene regulation also allows cells to react quickly to changes in
their environments. Although we know that the regulation of genes is critical
for life, this complex process is not yet fully understood.
Gene regulation can occur at any
point during gene expression, but most commonly occurs at the level of
transcription (when the information in a gene’s DNA is passed to mRNA). Signals
from the environment or from other cells activate proteins called transcription
factors. These proteins bind to regulatory regions of a gene and increase or
decrease the level of transcription. By controlling the level of transcription,
this process can determine when and how much protein product is made by a gene.
Lactase deficiency is believed to
be genetically programmed to produce this protein enzyme lactase that breaks
down milk sugar lactose into lactic acid and other products. Its ability
to do this is age-related as the LCT gene responsible for the production of
lactase becomes progressively latent with time. According to some studies LCT
genes remain active between the ages of 5-20 years.
It was once thought that
genes do not change. But recent research in the field of epigenetic
showed that genes do change in response to the environment, and they are
capable of changing their cellular behaviour including the social behaviour of
the individual. It is the case of nature vs nurture. In fact, it is their
ability to change especially to the environment as a stimulus that is the very
reason how all living organisms begin to adapt for the better. This is not
something new as we think.
As far back as in 1864 Herbert
Spencer in his “The Principles
of Biology” looked at Darwin’s evolution as “Function, Adaptation and
Variation” of the various species of life where he introduced the expression
'survival of the fittest', in the sense of 'the most appropriate to its
environment'. Scientists have only recognized this behaviour and adaptive
changes only recently, and they gave it the name of this new study called
‘epigenetics’.
Epigenetics is the study of
the environment and its impact on behaviour, and how the changing environment
affects the way the genes are going to express themselves. Gene expression
means the process by which the information encoded in a gene is turned into a
function. This mostly occurs via the transcription of RNA molecules that code
for proteins or non-coding RNA molecules that serve other functions.
Unlike genetic changes, epigenetic
changes are reversible and do not change the DNA
sequence, but they can change how the body reads a DNA sequence.
Another way of explaining this is, the environment influences the behaviour
of our genes and how they work for us, even though the environment does
not change the DNA sequence, but they can change how the body reads a DNA
sequence to change the way we behave and react.
For example, a pair of identical
twins born from birth but brought up separately in different environments
and social influences may have entirely different social characteristics and
behaviour though their physical features remain identical.
In the same way we may explain why
two identical twins or as in your brother case, and yourself as a sister, your
brother is drinking milk persistently till age of 41, and he becomes milk
tolerant, whereas with yourself who does not, becomes intolerable to milk and
lactose. This may be due to adaptation when your brother is constantly exposed
to the same dietary environment that induces the LCT gene that produces lactase
to remain active lifelong, whereas for others like yourself where milk was
switched off in favour of other foods, has caused the lactase-producing genes
to switch off when no longer stimulated or needed.
Hence, it is not surprising to me that your eldest brother, though has
genes similar to yours, has adapted for the better by stimulating his genes to
adapt to milk drinking since a baby till he is now 41 years, whereas your
similar parental genes have not. I suppose your parents may have traditionally
been feeding him milk since a baby 15 years earlier than yourself since social
behaviour does change over just one generation from past traditions to recent
trends, and that could have affected the genes to continue to express the
enzyme lactase to break down the lactose in milk.
This is precisely what I mentioned earlier in my article on milk
intolerance that milk (milk sugar lactose) affects mainly the Asians,
predominately the Chinese whose mothers took off their babies from milk far too
early after one year instead of allowing them to continue with milk as a
supplementary food after weaning them to other foods. The problem about
nutrition is, it is such a complex mixture of
scientific-medical-social-economic-behavioral-anthropological field of study
that we know so little about their interactions, such as what food is exactly
right for us, or when to switch over from milk to other foods. We must bear in
mind milk like eggs for a developing chicken that is still incubating inside
the eggs for 21 days is the only food for the chick, as with milk as the only complete
food for all mammalian babies including human babies.
In fact, nutritionists recommend that a baby should be given other foods as
early as 6 months, although they did not actually suggest that milk should not
be given after 6 months. In other words, the nursing period of 6 months does
not necessarily mean that milk should not be drunk after that, bearing in mind
milk is still the complete food rich in all nutrients that could support the
growth of a body till even well past one year, not just for 6 months as
nutritionists recommend. I have seen children drinking milk even at 5 years old
and they look very healthy and active. Perhaps milk may not have sufficient
calories to support the energy requirements of a growing child. Milk is so good
and complete in nutrients that calves that are much heavier and stronger than
human babies feed on them from mother cows till it becomes almost an adult cow,
buffalo or a bull. These animals, as with all other mammals that feed their
young till they can thrive on their own food, have no problem with milk or
lactose intolerance, only humans. I suppose our busy commercial and economic
lifestyles are such that we have no patience in breastfeeding or to continue to
bottle-feed our babies as long as they want the milk.
Human milk contains 3%--5% fat,
0.8%--0.9% protein, 6.9%--7.2% carbohydrate calculated as lactose, and 0.2%
mineral constituents expressed as ash. Its energy content is 60--75
kcal/100 ml.
The energy requirement of a child
from 1 - 5-year-old is generally 100cal/kg/day between 1 to 3 years old, 80
kcal/kg/day, between 4 to 5 years, and 70 kcal/kg/day, 6 to 8 years needs 60 to
65 kcal/kg/day from 6 to 8 years, and for 9+ years he / she needs between 35 to
45 kcal/kg/day. Our problem is that food is like medicine. We know a lot of
things in medicine, but surprisingly a lot of information on nutrition remains
unknown to us. So, milk alone may not be sufficient in quantity to support
accelerated growth in a child, and other foods need to be supplemented after 6 months
of weaning.
In medicine, drugs are used, and we
know a tremendous lot how they react in the body (pharmacodynamics) and how the
body deals with them (pharmacokinetics) because all drugs are just pure organic
compounds, mostly synthetic, and we can easily trace their pathways in the body
– how they are metabolized and excreted from the body. But with food as a
medicine, especially plant-based, they contain tens of thousands if not
millions of phytochemicals and medicinal values, not just nutritional values in
them.
Furthermore, if they are eaten in a
wide variety, how are nutritionists and nutritional scientists going to know
how they are going to react in the body, let alone their phytochemicals
reacting and cross-acting with each other on ingestion? It is almost
impossible to know or to trace their metabolic pathways. That is the
reason we often receive all kinds of unsubstantiated health, often
contradictory health-protective, or health-damaging claims about foods in
videos, WhatsApp, advertisements, health magazines, newspapers and in social
media. Everyone is taking advantage of our ignorance.
Nutritionists now call foods that
have other nutritive or medicinal functions as “functional foods” defined as
foods that contain, in addition to nutrients, other components that may be
beneficial to health or have a potentially positive effect on health or their
medicinal therapeutic values beyond basic nutrition.
Traditional standard food
composition tables give us the nutritive valves of the major food chemical
components – carbohydrates, proteins, fats, vitamins, and minerals. Some food
tables provide us values of trace minerals as well. But none of the food
composition tables tell us anything about “non-nutritive” substances, yet
health-protective principles in them – the tens of thousands of
naturally-occurring phytochemicals and their protective or medical properties
bestowed by Nature for us as medicines as well. It is almost impossible for any
analytical food scientist to analyse them all, let alone for nutritionists to
study their health impacts on the body.
The National Institutes of
Health (NIH) is the largest funder on health issues, with nutrition
research investments estimated at $1.9 billion annually (5% of total
NIH funding) for fiscal year 2019. Approximately 25% of this funding (1.3% of
total NIH funding) focuses on diet for the prevention or treatment of disease
in humans, and yet we know so little about how food can affect the body and
health. This is only in America. World-wide nutrition research takes precedence
over all other medical research. World-wide it is estimated the annual expenditure
spent on nutrition research exceeds US 100 billion dollars resulting in an
avalanche of research papers published with a bit of inroads made on how food
affects our health and on latency of diseases yet to come, yet we still
know only a little. Nutrition for health is probably the most favourite and popular subject ever written very often in women and man magazines, and widely discussed in all print and electronic media including on television and on radio, including messages and information circulated in WhatsApp chat groups.
Only cancer research at US$2.9
billion in 2020 exceeded that of nutrition research. Previously it was
nutrition and nutrition research that occupied the central stage in health
care. These are the only two areas, cancer and nutrition research that are
given the highest priorities in medical research and yet we cannot completely
solve problems on disease under these two fields. Let’s take just these two
examples: nutrition and medicine.
In medicine for instance, we know
the dosage of the drug to give. We can titrate the dose to the patient’s needs.
We can adjust it to a person's body weight up to the maximum dose allowed
according to the drug manufacturer’s instructions.
But with food it is so complicated
that we only have some idea how much nutrient intake to recommend, but not give
to an average person. Nutritionists call this as “Recommended Daily Allowances
(RDA). We can only recommend a certain plus and minus allowance because
we do not know exactly how much intake is needed for each nutrient for optimal
health. It varies so much for individuals according to their age, sex, physical
activities, childbearing or not, genetic make-up (ethnicities), body size and
weight and even their health status.
Even for health we cannot give any
specific or single definition. W.H.O. in its Constitution gave a very
broad holistic definition of health as “a state of complete physical, mental
and social well-being and not merely the absence of disease or infirmity” That
definition does not even tell us or explain what then “optimal health” is?
Thus, the recommended daily
allowance for food intake is based on numerous studies done on as huge a
population who are in apparently good health, and the average taken based on so
many influencing factors such as age, sex, morbidity and mortality, food
consumption, types of foods and quantities consumed, metabolic activities,
active and sedentary lifestyles, disease patterns, and so on. These
recommendations are not even fixed. In most countries they are revised every 5
years by a huge committee of highly powered medical and nutrition experts
because nobody knows the precise “dosage” for nutrient requirements, unlike we
do for drugs.
The RDA is the average daily
dietary intake level that is sufficient to meet the nutrient requirement of
nearly all (97 to 98 percent) healthy individuals in a particular life-stage
and gender group. The RDA is the goal for usual intake by an individual.
The RDA depends not only on age,
gender, physical activities, but also on environment temperatures, food
availability, social, cultural, personal, psychological, economic factors, let
alone state of health, beliefs, food taboos among others. It is a highly,
highly complicated problem so unlike in medicine where problems on disease,
drugs indicated, and dosages are so clear cut to us.
Coming back to the nutritional
problem, what strategy can we implement to solve, if not reverse lactose and
milk intolerance. Perhaps one answer is, we can use lactose-breaking
bacteria found in the colon (beneficial human microbiota – the
colonic microbiome) that has endogenous lactase activity,
These bacteria can break down
lactose (milk sugar) into lactic acid. Some of these lactose-bacteria
called Lactobacillus and Bifidobacterium,
especially Lactobacillus bulgaricus and Streptococcus thermophilus are
also found in yoghurt. They possess beta-galactosidase activity (bacterial
lactase) that allows them to digest and utilize lactose. These bacteria
hydrolyse the lactose to glucose and galactose and subsequently ferment them to
lactate, short-chain fatty acids (SCFAs), and gases, such as H2, CO2,
and CH4 Although Bifidobacterium bifidum expresses
lactase activity, no clinical trials have determined its impact on
lactose-intolerant subjects.
Unfortunately, in normolactasia
(normal lactate), when intestinal lactase is high, only a small percentage of
ingested lactose reaches the colon.
Lactose cannot be directly absorbed
in the intestinal tract and must, instead, be broken down into its two smaller
component sugars by an enzyme called lactase and hence they cause intestinal
disturbances if they stay there unbroken down and unabsorbed. Normally,
the activity of the LCT gene that produces
lactase, LCT, declines after infancy. Recent evidence suggests that a
decline occurs not because the genetic code is changed, but because the DNA
is chemically modified so that the lactase gene is switched off
due to shut down of dietary influence. The epigenetic modification
that turns off the lactase gene does not happen
in lactose-tolerant individuals like your brother who constantly drinks
milk. This observation is crucial in understanding how lactose intolerance
develops with age.
Recent studies have shown that
the symptoms of lactose intolerance can be alleviated in some people
by changing the population of their intestinal microbiome by transferring
lactose-digesting bacteria such as yogurt in them. The adaptation of the intestinal
microbiome may explain why some ancient pastoral populations with no
genetic evidence of lactase persistence tolerated milk and dairy products.
We think that giving lactic acid
bacteria such as yogurt and fermented products regularly as a
probiotic can ease the symptoms of lactose intolerance, because these
bacteria may not persist in the colon. One promising new strategy is to give
the lactic acid bacteria a complex sugar that they can digest but humans cannot
for them to remain in the colon. But this needs to be studied.
Another way I can think of, is to
use faecal microbiota transplantation (FMT) where a solution of faecal matter
from a milk-tolerant donor is introduced into the intestinal tract of a
non-milk tolerant recipient in order to directly change the recipient’s gut
microbial composition to confer a health benefit to someone who is milk
intolerant. That may be another good nutritional strategy we can work on.
In summary, lactase deficiency is
thought to be genetically programmed and age-related as the gene that is
responsible for the production of lactase (LCT gene), becomes dormant
progressively with time. It tends to appear between the ages of 5-20 years and
may be prevented through epigenetic influence by regularly drinking milk.
As a last note, let me tell you
that I too am milk intolerant if milk is drunk more than 500 ml in one sitting.
Perhaps my ICT gene is still active by putting milk regularly in smaller
quantities into my tea, coffee, and cocoa-based beverages, though slowed down
and the lactase expressed is insufficient to deal with more than 25 g of
lactose in 500 ml of pure milk if drunk in one go.
I hope I have explained to you
Sussie Chan
(A 3,297 worded answer in 10 pages)
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