After years of research, cancer remains an
enigma. It’s certainly a label that covers many diseases and one size doesn’t
fit all, but we also know that obesity and processed foods somehow play a key
role—and all the clues are pointing at an unlikely culprit. Insulin, the
life-saving hormone released by the pancreas to lower blood sugar (glucose) levels,
is evidently an accessory to cancer.
New breakthrough studies, published over
the last couple of years, are discovering that insulin helps tumours of all
sorts to develop and grow, especially in the case of breast and prostate
cancers. The hormone is usually seen as part of a vital process for maintaining
a healthy life—just ask any type 1 diabetes sufferer who has to have regular
injections of insulin to stay alive—but it can also aid and abet a killer.
Insulin and diet
Cancer specialists are only just beginning
to recognize the role that insulin is playing in the develop-ment of cancer,
and they believe that it’s a characteristic of being overweight and obese. But
other evidence suggests that they have it round the wrong way: high insulin
production, or hyperinsulinaemia, can lead to obesity, and such a state is a
direct result of eating processed foods. If that is so, then this is the
strongest evidence yet that our modern Western diet is a major cause of cancer.
Insulin normalizes blood sugar levels, and
it also helps body tissues to grow by either signalling growth or increasing
levels of hormones that directly affect growth, an essential mechanism
involving what are known as ‘insulin-like growth factors’ (IGF).
But this growth-stimulating process doesn’t
only aid normal, healthy growth and development; it also appears to be a
co-worker with cancer towards the development of tumours when the pancreas
produces an excess of insulin. Researchers have noted, for example, that people
with cancers of the colon, breast and prostate have high levels of IGF
circulating in their blood. Indeed, it has been established that IGF can be
found in around 80 per cent of all cases of lung cancer (Neoplasia, 2009; 11:
672–82).
Most oncologists believe that insulin resistance
is a direct result of obesity, but researchers are now finding a direct link
between it—and hyperinsulinaemia—and carbo-hydrates, the huge food group that
includes cereals, vegetables, glu-cose, fructose and sucrose. When
carbohydrates were reduced or entirely eliminated from the diet, it was found
that tumour growth was either slowed or stopped completely.
But the answer doesn’t appear to be that
simple. Other researchers have suggested that eliminating an entire food group
will, in the long run, cause as many health problems as it solves. One study by
the Rowett Research Institute in Aberdeen, Scotland, found that a
low-carbo-hydrate diet also reduced levels of the fatty acid butyrate in the
gut, which offers protection against colo-rectal cancer (FEMS Microbiol, 2002;
217: 133–9).
As Professor Harry Flint, the research team
leader, has said: “In the long run, it’s possible that such diets could
contribute to colorectal cancer”.
One of the best-known examples of the
high-fat, low/no-carbohydrate approach is the Atkins diet, and its critics
report that those who stay on the diet are also increasing their chances of
developing heart disease (J Am Diet Assoc, 2009; 109: 1263–5).
And not all carbohydrates are bad for you.
Scientists at the Burnham Institute for Medical Research in La Jolla,
California, have recently discovered that complex sugar molecules known as
‘glycans’, a complex carbohydrate, appear able to suppress tumour growth (Proc
Natl Acad Sci U S A, July 8, 2009; doi:10.1073 /pnas.0904515106).
The mistake appears to lie in treating all
carbohydrates the same when, in fact, they come in many different
varieties—from the single-molecule (monosaccharides) carbo-hydrates, such as
glucose, fructose and galactose, and the two-molecule (disaccharides)
carbohydrates, such as sucrose, lactose and maltose, to the multichain
molecules (polysac-charides), which are the starches found in cereals,
potatoes, root vegetables, seeds and pulses.
Most processed carbohydrates, which include
white rice, white bread, biscuits and cakes, contain high levels of glucose, as
measured by their glycaemic index (GI). The more high-GI carbohydrates we eat,
the more insulin the pancreas has to produce to normalize the blood sugar
ratio. As a result, most of us who are living on a Westernized, processed diet
will suffer to some degree from hyperinsulinaemia. This can be a direct
response to a high-GI diet or, because we have become insulin-resistant as a
result of our diet—which is often the beginnings of type 2 diabetes—the pancreas
will attempt to compensate with an overproduction of insulin. In either case,
the excessive production of insulin evidently has two major effects:
- it
is a cause of obesity, and
- it
increases the risk of cancer.
Insulin–cancer
connection
Researchers in Italy were among the first
to make the connection between high-glycaemic carbohydr-ates and breast cancer.
In a study of 2569 women with breast cancer, who were compared with 2588
healthy controls, the scientists discovered that the women who regularly ate
high-glycaemic carbo-hydrates, such as white bread, doubled their risk of
breast cancer, whereas the effect was neutral among those who ate carbohydrates
that had a more moderate GI score (Ann Oncol, 2001; 12: 1533–8).
Two years later, the leading oncologist Dr
D. Barry Boyd, at the Greenwich Hospital in Connecticut, suggested that insulin
and IGF might speed the cellular growth of cancers—especially breast cancer. He
also suspected that high levels of IGF might even interfere with chemotherapy,
causing it to be less effective (Integr Cancer Ther, 2003; 2: 315–29).
This theory was tested a year later, when
researchers from the Brigham and Women’s Hospital and Harvard Medical School in
Boston profiled the breast cancer risk in a group of 475 women, aged 20 to 75
years, who were living in Mexico. Those who were eating the most carbohydrates
were up to three times more likely to develop breast cancer compared with those
who ate the lowest amounts in the group.
There were several compelling reasons why
the researchers chose to study Mexican women. While carbohydrates have always
formed a principal part of the Mexican diet, it’s only been in recent years
that the levels of obesity in Mexico have increased dramatically.
The main carbohydrates the women were
eating were fructose and sucrose. Although fructose is one of the lowest GI
foods, sucrose—found in sugar and many other processed foods—is among the
highest. The carbohydrates, and not the fats, were apparently the cause of the
increased risk of breast cancer, the researchers concluded (Cancer Epidemiol
Biomarkers Prev, 2004; 13: 1283–9).
Another piece of the jigsaw was discovered
only three years later, when researchers found that a low-carbohydrate diet
significantly decreased the growth of brain tumours in mice (so it may not
necessarily apply to humans). The research team, from the biology department of
Boston College in Massachusetts, used a commercially available powdered food
substitute called KetoCal—developed to treat children with epilepsy—that is
high in fats (72 g) and low in carbohydrates (3 g). In mice, this diet
decreased the growth of brain tumours by between 35 per cent and 65 per cent,
and the survival rates in the mice on the special diet were also much higher.
The researchers reckoned its success was because the diet “starved the brain
tumour cells of the sugary molecules on which they rely for growth and
survival” (Medical News Today, 26 February 2007; www.medicalnewstoday.com/
articles/ 63544.php).
These findings have been supported by
another study involving laboratory mice this year. This time, the mice had
prostate cancer and, again, a high-fat, low-carbohydrate diet slowed the growth
of tumours. Lead researcher Stephen Freedland, a urologist at the Duke Prostate
Center in Durham, NC, reported that the low- or no-carbohydrate diet
significantly lowered serum insulin levels, thereby slowing tumour growth
(Cancer Prev Res, 2009; 2: 557–65).
Freedland and his team are currently
recruiting human subjects for another trial involving low carbohydrates and
prostate cancer. “It’s very exciting—this is a potential new mechanism to fight
prostate cancer growth and help patients live longer with their disease,” he
said.
However, perhaps the most compelling
evidence has been gathered by the researchers who profiled a subgroup of 1651
post-menopausal women from the US-based Women’s Health Initiative Observational
Study, half of whom had breast cancer. After taking blood samples, the
researchers found that those women who had the highest insulin levels were
nearly 50 per cent more likely to have breast cancer compared with those who
had the lowest insulin levels.
“Women with the highest insulin levels in
their blood were more than two times more likely to develop breast cancer,”
said lead author Marc Gunter, from the Albert Ein-stein College of Medicine of
Yeshiva University, in New York. Although the ovaries stop producing oestro-gen
after the menopause, such women can have higher levels of insulin, especially
if they are obese (J Natl Cancer Inst, 2009; 101: 48–60).
Obesity–cancer connection
Researchers have known for years that
obesity, or a body mass index (BMI) greater than 30 kg/m2, is somehow related
to cancer. In a major report published in 2002, the authors found that people
who were obese or seriously overweight had a far higher risk of developing
cancers of the colon, breast—especially if the woman was also
postmeno-pausal—endometrium (the lining of the uterus), kidney and oesophagus.
They also pointed out that there was a highly probable connection between
obesity and cancers of the gallbladder, ovaries and pancreas, although the
evidence for this was not so clear-cut. Indeed, overall, obesity may be the
cause of 25–30 per cent of all colon, breast, endometrial, kidney and
oesoph-ageal cancers (Vainio H, Bianchini F. IARC Handbooks of Cancer
Prevention. Lyon, France. IARC Press, 2002).
In the US, around 41,000 new cases of
cancer each year are considered to be directly related to obesity, representing
3.2 per cent of all new cases (Cancer Detect Prev, 2003; 27: 415–21). Another
report reckoned that 14 per cent of all deaths from cancer in men, and 20 per
cent of those in women, are due to obesity and being overweight (N Engl J Med,
2003; 348: 1625–38).
If these statistics are correct, then they
clearly represent a major health problem, as nearly one-third of adults in the
US, for example, are now classified as obese (JAMA, 2002; 288: 1723–7), an
increase of 8 per cent in just eight years, while 15 per cent of children and
adolescents up to 19 years of age are also obese, numbers which have trebled
over the past 20 years (JAMA, 2002; 288: 1728–32).
Nevertheless, such a direct obesity–cancer
connection appears to be overly simplistic. If obesity on its own were a major
cause of cancer, then more than 41,000 obese people each year would develop the
disease. Also, as there are about 218 million adults in the US, this suggests
that around 72 million of them are obese, and only 0.06 per cent of these
individuals are developing cancer every year.
Most cancer and health information groups
agree with the current view that obesity is primarily the result of a sedentary
lifestyle coupled with a diet that is high in calories or fat (J Nutr, 2003;
133 [11 Suppl 1]: 3827S–9S; Cancer Epidemiol Biomarkers Prev, 2001; 10:
287–301).
However, nutritional researcher Michel
Montignac, who gave his name to his own GI diet, believes that the extent of an
individual’s hyperinsulinaemia also determines the extent of the obesity.
“What distinguishes the person who is overweight
from the person who is slim is that the latter has a pancreas secreting just
the right amount of insulin to bring a raised blood-sugar level down to its
normal value. The overweight person does not. Instead of releasing the right
amount of insulin, the pancreas will secrete more—sometimes much more—than is
required to take sugar present in the blood down to its normal level,” he says
(Montignac M. Eat Yourself Slim. London: Montignac Publishing, 1999).
In its turn, hyperinsulinaemia initiates a
metabolic process known as ‘lipogenesis’, where the body stores abnormally
large amounts of fat instead of allowing it to be oxidized and ‘burned’ for
energy. This means that an overweight person will tend to store fat because of
hyperinsulinaemia or insulin resistance which, in turn, is caused by either a
weak pancreas or a diet that is rich in high-glycaemic carbohydrates (Montignac
M. Eat Yourself Slim. London: Montignac Publishing, 1999).
In a small study of 23 women, insulin
resistance was reduced when they were put on a diet that was “moderately lower
in carbohydrate”, suggesting that it is a problem that can be improved just by
restricting carbohydrates (Asia Pac J Clin Nutr, 2008; 17: 669–71).
For Montignac and others,
hyper-insulinaemia and insulin resistance lead to obesity, and can be a cancer
risk, an idea diametrically opposed to the current view that obesity causes
insulin resistance.
Warburg’s sugar theory
Montignac’s approach ties in with another
theory of cancer that is finally beginning to gain credence some 80 years since
it was first postulated: Otto Warburg’s sugar theory. Dr Warburg (1883–1970),
an outstanding German biochemist whose work focused on intracellular
respiration, photosynthesis and cancer, observed that healthy cells use oxygen
to break down glucose from carbohydrates, which releases energy, whereas cancer
cells appar-ently obtain energy from a process he referred to as
‘fermentation’—better known today as ‘glycolysis’—a process of extracting
energy from glucose without the use of oxygen.
“The prime cause of cancer is the
replacement of the respiration of oxygen in normal body cells by a fermentation
of sugar,” Warburg said in a lecture to Nobel laureates in 1966, four years
before he died.
Despite winning him the Nobel Prize for
Medicine, his sugar theory was largely ignored until just recently. A study
from the University of Arizona revealed that radiologists can use the extent of
glycolysis to determine the stage of development reached by a tumour. According
to the researchers, an increased break-down of glucose is a “near-universal
property” of cancer (Nat Rev Cancer, 2004; 4: 891–9).
Furthermore, cancer cells are known to have
10 times more insulin receptors than do healthy cells (Cell Commun Signal,
2009; 7: 14), which may explain why it is that insulin helps the growth and
development of tumours.
The end in sight
Nutritionists have been telling us that
processed, ‘white’ carbohy-drates are bad for us, but it’s never been made
clear why that is nor what happens when we eat these foods. However, by piecing
together several disparate strands of research, the picture is finally becoming
clearer: these processed foods raise our insulin levels, an inevitable reaction
in order to reduce the large amounts of blood sugar, or glucose, brought about
by carbohydrates that have a high GI score such as white bread, white rice,
biscuits, cakes and ‘fast foods’.
People who regularly eat pro-cessed foods
will eventually go on to develop either hyperinsulinaemia or become
insulin-resistant; as a result, the pancreas consistently produces an excessive
amount of insulin. This overproduction has two serious consequences: it can
make us obese; and it can encourage the growth of cancer cells, which feed off
of the insulin.
At this time, oncologists appear to be
looking down the wrong end
of the telescope. They believe that obesity
causes the insulin resistance or hyperinsulinaemia that, in turn, can cause
cancer. Yet, if they were to see it the other way round, the implications for
the processed food industry could be devastating—and long overdue.
Bryan Hubbard
Insulin therapy and cancer
If naturally produced insulin can boost
cancer growth, does the same apply to the insulin therapy that’s used by those
who have type 1 diabetes?
In fact, four new studies have found that
insulin therapy does indeed increase the risk of cancer, and three of these
reports implicate Lantus (insulin glargine), an injectable insulin analogue
derived from human insulin.
One of the studies, which involved 127,031
German patients with type 1 diabetes, found that the risk increased in relation
to the insulin dose. This means that, at the top end, those injecting 50 IU
daily have a 1.3 times greater risk of developing cancer than do healthy people
who are producing their own insulin (Diabetologia, 2009; doi:
10.1007/s00125-009-1418-4).
A different study, this time involving
114,841 type 1 diabetes sufferers
in Sweden, found that the risk associated
with insulin glargine varied according to the cancer: for breast cancer, the
therapy nearly doubled the risk whereas it was only marginal for prostate
cancer (Diabetologia, 2009; doi: 10.1007/s00125-009-1444-2).
Lantus, manufactured by Sanofi-Aventis, has
been used by diabetics ever since it became available in 2000, although concerns
over a possible cancer risk were raised in Germany following a survey carried
out among the policy holders of a private health-insurance plan. The survey
revealed that there was one new case of cancer for every 100 users of Lantus
and that the risk was dose-dependent.
Nevertheless, the European Association for
the Study of Diabetes (EASD), which commissioned the four studies, is urging
diabetics to continue using Lantus until more studies are carried out.
However, the cancer-causing qualities of
Lantus may have been known within weeks of its approval. According to Ernst
Chantelau, at the Diabetesambulanz MNR-Klinik in Dusseldorf, Germany, the
therapy was known to be highly mitogenic—causing cell proliferation—even before
it was approved by the European Medicines Evaluation Agency (EMEA). The
manufacturer told the EMEA ‘orally’ about the therapy’s mitogenicity, but the
EMEA dismissed the comment as ‘irrelevant’. However, at around the same time,
independent researchers were also discovering that Lantus caused cells to
proliferate when tested on human cancer cells. Research team leader Peter
Kurtzhals said that the therapy increased insulin growth factors (see main
story) by between six- to eightfold
(Diabetes, 2000; 49: 999–1005).
And Lantus is not the only insulin therapy
that’s been associated with cancer risks. In 2008, Pfizer announced that six
cases of lung cancer had been associated with its inhaled insulin therapy
Exubera. Although the company denied any causal link, the therapy was withdrawn
from the market in 2007 (Diabetologia, 2008; 51: 1–5).
The GI scores of some common foods
Only some carbohydrates stimulate excessive
insulin production. These are known as the ‘high glycaemic-index (GI) foods’ as
they contain an excess of glucose that has to be normalized by insulin.
Glycaemic levels can also be altered by the cooking process. Raw carrots, for
example, have a far lower GI score than cooked ones.
High GI foods
Beer (maltose) 110
Glucose 100
Roasted potatoes 95
Chips
95
Rice flour 95
Modified starches 95
Mashed potato 90
Crisps
90
Honey
85
Hamburger buns 85
Carrots (cooked) 85
Corn Flakes
85
Popcorn 85
Easy-cook rice 85
Rice cakes
85
Puffed rice
85
Low GI foods
Garlic
15
Courgettes
15
Aubergines
15
Tomatoes
15
Green vegetables 15
Apricots (fresh) 15
Peanuts 15
Soy 15
Fructose
15
Dark chocolate 20
Split peas
20
Lentils (green) 22
Sugar-free jams 22
Soy vermicelli 22
French beans 30
Fresh fruit
30
From Montignac M. Eat Yourself Slim.
Montignac Publishing, London: 1999
Insulin, the good and the bad
Without insulin, we would die. People with
type 1 diabetes—in whom the pancreas is no longer able to produce insulin—are dependent on an injectable form
of insulin in order to live. Without a daily injection of an insulin analogue,
the diabetic’s blood sugar would rise and the body would begin to burn up its
fat stores. Within a few days, this leads to the life-threatening condition
known as ‘diabetic ketoacidosis’.
However, an individual who suffers from
hyperinsulinaemia, where the pancreas produces too much insulin, will have
too-low levels of blood sugar, a condition known as ‘hypoglycaemia’. Its
symptoms include pale-ness, shaking, shivering, perspiration, rapid heartbeat,
hunger, anxiety and blurred vision. It can also cause convulsions.
People with type 2 diabetes—the stage
before type 1, as around a third of all type 2 sufferers will eventually need
insulin therapy—often have insulin resistance, where the cells have become
resistant to the effects of insulin. Initially, the pancreas attempts to
compensate by producing more insulin but, eventually, the pancreas proves
unable to cope.
Vol. 20 05 August 2009