This turned into a pretty long article, so I’m going to provide a summary up-front for those of you who are time-challenged:
- Genetics play a significant role in type 2 diabetes and obesity;
- but, recent evidence shows that genetics alone don’t cause diabetes without environmental triggers and a leaky gut.
- The bad news is that almost everyone is exposed to these triggers and leaky guts are not uncommon;
- but the good news is that a leaky gut can be healed, which may slow or even reverse the autoimmune process that causes type 2 diabetes.
So far in this series we’ve looked a model of understanding diabetes and obesity as autoimmune, inflammatory diseases. We’ve explored how obesity contributes to diabetes, and how insulin resistance contributes to obesity. And we’ve seen that, while diabetes and obesity often go hand in hand, that isn’t always the case; even skinny people get type 2 diabetes.
I hope you’re aware by now that obesity and diabetes are not simply diseases of sloth and gluttony. Nor are they caused by eating too many carbohydrates (more on this later). You’ve probably also noticed that some people get fat and stay fat despite exercising regularly and not eating much, while others can eat ridiculous quantities of food, never exercise and stay lean.
Obviously there are other factors at work here, and that’s what we’re going to talk about in this article. Specifically, I’m going to address the role of genetics as a risk factor for diabesity. There’s absolutely no question that genetics do play a significant role in both obesity and diabetes. To some extent genetics explain the apparent paradoxes I mentioned in the previous paragraph. But it’s equally important to understand that being genetically predisposed to develop diabesity doesn’t guarantee that you will. In fact, recent research suggests that other environmental and physiological factors must be present to activate the genetic patterns.
The triple whammy of genes, toxins and a leaky gut
In the second article in this series, I presented evidence that obesity and diabetes are autoimmune, inflammatory disorders. This is important to understand, because it suggests that we can learn more about what might cause these conditions by studying other autoimmune diseases. Autoimmunity is one of the hottest topics in the scientific literature. And although there’s still much we don’t understand, significant progress has been made over the past two decades in illuminating the mechanisms involved in autoimmune disease.
One of the heavyweights in the field is a researcher named Alessio Fasano. In 2009 he published an article in Scientific American called “Celiac Disease Insights: Clues to Solving Autoimmunity“. Fassano argues that all autoimmune diseases – not just celiac disease – involve a triad of factors: genetic susceptibility, an environmental trigger and a gut abnormality. Each of these is a risk factor for autoimmunity on its own, but Fassano’s work shows that those who go on to develop full-fledged autoimmune diseases (including diabesity) almost always have all three.
This theory – which is well supported by the evidence, as we’ll see – makes perfect sense when you understand the principles of epigenetics. Up until very recently, scientists believed that the affects of nurture (environment) on a species’ nature (genes) took generations to develop. Darwin’s Origin of Species taught us that evolutionary changes take place over millions of years of natural selection, not in a single lifetime. But recent work by pioneers like Dr. Lars Olov Bygren of the prestigious Karolinska Institute in Stockholm has shown that powerful environmental triggers can bypass evolution and pass traits on in a single generation.
Epigenetics is the study of gene activity that doesn’t involve changes to the genetic code, but still gets passed down to at least one successive generation. These inherited patterns of gene expression (known as the “epigenome”) hover above the genome and are what determine whether your genes get switched on or off, and at what intensity. This epigenetic blueprint determines what affect environmental factors like diet, stress and toxins will have on genes passed from one generation to the next.
What this means is that, yes, genes are important. But it also means that the genes that might predispose us to develop conditions like diabesity may only be activated in the presence of environmental triggers like poor diet, toxic chemicals and a leaky gut. In the sections to follow we’ll look at each factor in the “genes-toxins-gut” triad in more detail.
Are there genes for diabesity?
There is no question that genes contribute to both obesity and diabetes. Studies on identical twins have shown an 80% concordance for type 2 diabetes (T2DM). That means that if one twin develops T2DM, there’s a 4 out of 5 chance the other one will too. And lest you think this might be described by something shared in the twins’ environment, there is no such concordance between fraternal twins.
That said, 1 in 5 of those identical twins carrying the same genes didn’t become diabetic, so there is clearly an environmental factor at work as well. This is exactly what you’d expect to see if you’re familiar with epigenetic principles.
There’s now a very long list of genes associated with T2DM and obesity, including TCF7L2, HNF4-a, PTPN, SHIP2, ENPP1, PPARG, FTO, KCNJ11, NOTCh3, WFS1, CDKAL1, IGF2BP2, SLC30A8, JAZF1, and HHEX. (I can’t understand how geneticist’s brains don’t explode from acronym overload.) And studies pretty clearly show that the more of these genes you have, the higher your risk of diabesity. With each abnormal gene, beta cell dysfunction (which in turn compromises insulin production) gets worse. If you’re unlucky enough to have five of them, your beta cell glucose sensitivity and insulin production is likely to be up to 40% lower than a person without those genes. That’s no small difference.
Other studies have shown that genetic abnormalities predict T2DM independently of conventional risk factors, and that genetic defects in mitochondrial function cause insulin resistance in lean, otherwise healthy offspring of type 2 diabetics.
It’s not “nature versus nurture” – it’s “nature plus nurture”
We’ve seen so far that genes are a big factor in type 2 diabetes, but that not everyone with these genes develops diabetes. Environmental factors are the missing link that determine whether these bad genes get switched on and cause full-fledged diabesity.
So what might those environmental factors be? I’m just going to summarize them here, because many of them will be the subject of future articles in the series. They are:
- Your mother’s diet during pregnancy, as well as her gut flora and whether or not she had gestational diabetes.
- Your diet. In particular, how much refined carbohydrate, fructose and industrial seed oils you eat.
- Pesticides, herbicides and PCBs
- Environmental chemicals like arsenic and BPA
- Prescription drugs, especially antidepressants (SSRIs) and chemotherapy..
It seems that at least one of these environmental factors must be present for the diabetes genes to be activated. Take a look at that list. Those aren’t exactly rare. They’re ubiquitous. I’d venture to say that all people living in the modern world are affected to some degree by at least one of them. Even those who eat a pristine diet and avoid pharmaceutical drugs can’t escape the toxins in our water, air and (even) organic food. This, my friends, is why we have a diabetes epidemic on our hands.
“All disease begins in the gut.” – Hippocrates
The phrase “leaky gut” used to be confined to the outer fringes of medicine, employed by alternative practitioners with letters like D.C., L.Ac and N.D. after their names. Researchers originally scoffed at the idea that a leaky gut contributes to autoimmune problems, but now they’re eating their words. It has been repeatedly shown in several well-designed studies that the integrity of the intestinal barrier is a major factor in autoimmune disease.
This new theory holds that the intestinal barrier in large part determines whether we tolerate or react to toxic substances we ingest from the environment. The breach of the intestinal barrier (which is only possible with a “leaky gut”) by food toxins like gluten and chemicals like arsenic or BPA cause an immune response which affects not only the gut itself, but also other organs and tissues. These include the skeletal system, the pancreas (hint: diabetes!), the kidney, the liver and the brain.
Researchers have identified a protein called zonulin that increases intestinal permeability in humans and other animals. This led to a search of the medical literature for illnesses characterized by increased intestinal permeability (leaky gut). Imagine their surprise when the researchers found that many, if not most, autoimmune diseases – including celiac disease, type 1 diabetes, multiple sclerosis, rheumatoid arthritis and inflammatory bowel disease – are characterized by abnormally high levels of zonulin and a leaky gut.
They also found that gluten causes excess production of zonulin in certain people with a genetic susceptibility. This could explain why gluten directly contributes to leaky gut in certain populations.
What these discoveries have shown us is that genetic susceptibility and environmental triggers alone may not be enough to explain autoimmune disease. In order for environmental triggers to damage or activate faulty genes, a third factor must be present: a leaky gut.
Recent evidence has also revealed that the gut flora play a significant role in determining the permeability of the gut, and that diabetics and healthy people have significantly different gut flora (suggesting that dysregulated gut flora plays a role in diabetes).
One study showed that showed that the overall number of colonic bacteria between diabetics and non-diabetics was similar, but that the proportion of species was different. Diabetics tended to have higher numbers of Bacteroidetes and Prevotella, which are gram negative bacteria that produce molecules called lipopolysaccharide (LPS). And guess what? LPS is known for its potent stimulation of the immune system.
Consider a hypothetical woman with a few genes that predispose her to diabetes. She eats a typical American diet, which is full of refined flour, industrial seed oils and fructose. Her mother had poor gut flora, and chose to bottle-feed her instead of breast-feed, both of which contribute to poor gut flora and intestinal permeability. This poor woman is now a walking diabetes time bomb. Anytime she ingests a toxin – whether it’s gluten or a chemical – it leaks through her gut and has the potential to activate her diabetic genes.
The bad news is that this is an incredibly common scenario. The good news, however, is that this new theory (that genetic and environmental factors are only problematic in the presence of a leaky gut) has an upside. According to Dr. Fasano:
…once the autoimmune process is activated, it is not self-perpetuating; rather, it can be modulated or even reversed by preventing the continuous interplay between genes and environment. As tight junction dysfunction allows this interaction, new therapeutic strategies aimed at re-establishing the intestinal barrier function offer innovative, unexplored approaches for the treatment of these devastating diseases.
In other words, it’s possible that you can’t get type 2 diabetes without a leaky gut, and that by healing your gut the autoimmune process driving T2DM may be slowed or even reversed.
Pretty cool, huh?
A final note: it’s not exactly true that improving metabolic health by repairing a leaky gut is an “unexplored” approach. Plenty of “alternative” practitioners have been doing this for years. In fact, they pioneered the techniques at a time when researchers were still snickering at the idea of “leaky gut”. Just another reminder of the danger of academic arrogance.