Dr Alan Desmond is a Consultant Gastroenterologist and General Physician as well as a best-selling author. He has a passion for helping individuals improve their gut health whether they are one of his patients or one of his ~150k Instagram followers. He was kind enough to share his expertise around how to improve gut health such as foods to prioritise, avoid and the reasons behind this.

V-Land UK (V-L): Why do you recommend a plant-based diet? 

Dr Alan Desmond (AD): Very early on in my training as a doctor I became interested in gut health and I realised that when you explain diseases and medications and treatments to patients with gut health problems, they always ask you about food. So I wanted to have evidence-based answers for my patients. 

When you look at the evidence on digestive health, it is clear that food really does matter. 

If you want to eat for optimal digestive health, if you take these two principles forward, you'll do pretty well. Principle number one: go for whole foods, not processed foods. Principle number two go for plant sources of nutrition before animal sources of nutrition. 

The evidence very clearly pointed to me that this whole food plant-based approach has so much to offer in terms of protecting, improving, and safeguarding our digestive health.

V-L: The term ‘processed’ can be confusing, please explain what you mean by this?

AD: Perhaps, a better way to frame it would be to encourage individuals to use foods which are as minimally processed as possible, but to make it clear there is plenty of evidence that certain lightly- or moderately-processed foods such as extra virgin olive oil, cacao powder, milled linseeds, tofu and seitan can still be useful, beneficial and healthy things to eat. 

The term whole food can also be confusing. In the ideal situation, we're talking about fruits, vegetables, whole grains, legumes, nuts, seeds, all those good things. So when I'm talking to people about leaning towards whole foods, I guess what I'm really asking them to do is avoid junk foods. And for me, the defining characteristic of junk foods is the artificial additives. It's not so much about what's taken out of the food, it's what's put into the food. 

When we look at junk foods, they generally come in a packet and you'll see a long list of ingredients and realise pretty quickly that this highly processed food or ultra-processed food or junk food contains a lot of chemical additions that have no business in the human digestive tract: things like maltodextrin carrageenan, carboxymethylcellulose, polysorbase, and other artificial chemicals that have a measurable negative impact on our digestive health. So I'm really asking people to avoid junk foods with long lists of ingredients that you don't quite understand what they are because in general, at least some of those artificial ingredients are going to harm your digestive health.

The difference between a whole food and a junk food is the difference between an apple and an apple poptart. There are two extremes, they both have the word apple in them. But in terms of how your body treats them, how your digestive system treats and reacts to them, it's like night and day. 

V-L: So what came first? Your interest in gut health or plant-based nutrition? 

AD: Oh, gut health, of course. I qualified as a doctor back in 2001. When you're a young doctor, you work at different departments in the hospital, so you work in the dialysis unit, you might work on the care of the elderly ward, you might work for the orthopedic surgeons for a while, and you do a little bit of everything. It's a really busy time, and you're spending hundreds of hours in the hospital, night shifts with no breaks. It's a tough time. 

But during that period of time, I had my first rotation on the gastroenterology ward around 2003. And on the gastro ward, I realized that when your digestive system goes wrong, when your GI tract tips into a diseased state, your body is deprived of the fuel and the energy and the immune competence it needs to stay healthy. And that when patients have digestive health problems, their whole quality of life suffers. Most people with chronic digestive health symptoms feel that their quality of life is dreadful. In fact, there was a study a few years ago that showed that patients with chronic digestive health symptoms would give up on 15 years of their life expectancy for an instant cure for those symptoms.

Because food really matters to people. The ability to eat and enjoy and digest food really, really matters to people on a personal level, on a societal level, of course, not to mention the fact that the food you eat is actually the building blocks of your human body. So from a nutrition perspective, you need to be able to ingest, digest, absorb all of those great nutrients and put them to work. 

I realised very early on, during that period of time, that if you can specialise in helping people to improve their digestive health, you can revolutionise people's health and happiness. And for me, as a typically trained doctor, that began with medications, steroids, surgery, all those good things which I still practice today, but I realised very quickly that if we were going to really help people to protect, preserve and safeguard their digestive health for the future, we had to talk to them about food. And it was seeking evidence-based answers to the question: What should I eat doctor? That eventually, over a period of years, brought me to a whole food plant-based diet. 

V-L: From your answers so far it implies that even as a medically trained doctor who specialised in gastroenterology you didn’t have good evidence-based answers for the recurrent: What should I eat doctor?

AD: That's very true. When you're going through medical school (and I was in medical school for six years), and then I had postgraduate experience for another eleven years before I became a gastroenterologist, you've got a tonne of stuff to learn. It's essentially like learning a new language. First of all, you must learn the language of medicine, and then you have to learn about pharmacokinetics, disease states, virology, microbiology, biochemistry. The curriculum is vast and expansive. 

When I was in medical school 20 years ago, we learned about the building blocks of foods and their organic chemistry. We learned about proteins and carbohydrates and lipids. We learned about how those things contribute to the normal function of the human body and what severe deficiency states would result in. But 20 years ago we weren't really taught about the importance of food in health, which we now know is ridiculous because food is the number one driver of premature death and healthy years of life lost on this planet. But of course, it's been very encouraging in the last few years to see that starting to change in the UK. 

Now, the medical school curriculum includes, I think, about 15 competencies on food and health and how to talk to patients about food and learning about the importance of food for overall health. So that's incredibly encouraging. And work being done by groups which are bringing kitchen skills into medical schools is incredibly encouraging. 

Dr Alan Desmond

V-L: So, what particularly about an animal-based diet can contribute to gut dysbiosis? 

AD: I guess what we're talking about is the human gut microbiome. This has been an interest of mine since very early on in my medical career and I was lucky enough to work for a period at one of the world's leading gut microbiome research centres. There are a lot of other reasons why meat is so bad for your gut health without getting into the gut microbiome research.

Primarily, meat - particularly cooked meat - contains multiple chemicals and molecules that drive gut inflammation, gut barrier dysfunction, DNA damage, and even precancerous changes in the lining of the digestive system. And those would include things like heme iron, which is the form of iron that you only get from animal products, and certain genetically engineered vegan burgers.

We've also got HCAs, and PAHs which are strange chemicals that are generated when you expose meat to heat. So when you cook muscle, you generate these chemicals, which then are ingested into the digestive system by people who eat meat. And these are directly pro-inflammatory when landing in the gut.

Then you’ve got the nitrites, which can naturally occur in red meats, or are added to them as a preservative and also the high-fat content of animal products, particularly the high content of saturated fats and cholesterol. All of this is a perfect recipe for information barrier disruption, DNA damage, and precancerous changes. But when you look at the effect that eating these foods also has in the gut microbiome, it gets really worrying. 

The gut microbiome is something that we've only really learned a lot about in the last 20 years. And although there are literally dozens of research papers published every year, I still feel like we're just in our infancy of learning about what the gut microbiome does. 

So within your large bowel, you are carrying about 100 trillion microbes: little microscopic organisms, bacteria, viruses, yeasts, and archaea. And this system contains as many cells and 150 times more genetic material than the rest of your human body. You're mostly microbe by head count and genetic count. We are mostly microbe. We're not human at all, really! Part human. 

We're colonised by these bugs that are in the natural environment the moment we're born. And those bugs don't just sit there. They're biologically active. They help us to digest our first meal. They're crucial to the development of a healthy GI tract and healthy immune system. And as adults, they remain a control centre for human biology. This means that depending on the health of your gut microbiome, it's going to help tip you towards a state of health or a state of chronic illness. It's really important. The reason why that information is so empowering is because you can influence your gut microbiome every time you eat; you can dial the controls towards chronic inflammation and disease, or you can dial the controls towards healthy metabolic function and a lack of disease. 

It's incredibly important because the food that we eat is one of the main determinants of which microbes flourish and grow and reproduce within our gut microbiome and those populations of bugs that are flourishing are biologically active. They break down whatever we feed them and use that material to produce postbiotic substances, biologically active chemicals which are deep inside our body, interacting with the other components for gut microbiome, interacting with the lining of our gut, and in many ways entering our bloodstream and being biologically active throughout our body.

If you are eating a kind of standard Western meal which is made of meat, animal fat, doesn't contain very many plants, has processed carbohydrates, then the postbiotic substances you're generating, generally have a negative impact on human health. We call that the proteolytic microbiome. It's breaking down the product of excess protein ingestion. So you get things like secondary bile acids, ammonia, hydrogen sulfide, choline which are harmful substances: you get very little of the beneficial short-chain fatty acids, which is bad news because short-chain fatty acids are one of the key molecules in the human body that help keep us healthy. 

V-L: So when certain individuals transition to a more plant-based diet, they can experience, at least initially, changes in their guts such as bloating and gas. How would you suggest people cope with this transition?

AD: If you're moving towards a whole food plant-based diet, you are going to be increasing your intake of healthy foods: fruits, vegetables, legumes, whole grains, and nuts. So you are going to be making a lot of tremendously healthy changes. And the microbes in your digestive system and your digestive enzymes may need a few weeks to adjust to this new healthier approach to food. 

Typically, when people make this change, a couple of things will happen. Number one, their gut microbes will go crazy with all this wonderful diversity of plant fibre and start to ferment and produce beneficial postbiotic substances. But that also leads to an increase in gas and fluid production in our digestive system, which can make us feel a little bit bloated. 

Number two, you're going to start going to the toilet more often, you're going to see more poop, and you're going to see it more often. And that's a good thing. We know from studies, that people who eat a healthy high-fibre diet, may produce as much as seven times the stool volume of people who are eating a typical standard Western fibre-deficient diet. 

But take heart, because the evidence tells us everything settles down within about four to six weeks. If you are still finding it challenging and you are feeling that your digestive system isn't reacting too well to the sudden change in your approach to food, then good advice is just to take a step back, take a little break, and then come at it gradually. 

I would usually suggest that people start with breakfast. So for a week or two, they're having healthier, high-fibre breakfasts, such as oats or a good whole grain toast, banana, fruit, peanut butter. Work on those healthy breakfasts for a couple of weeks, then move on to lunch, then move on to dinner. But, some people eat a diet that is so low in fibre, they need to start even more slowly than that. So sometimes in extreme cases, I would ask people who don't eat any fruits, vegetables or whole grains to simply begin by snacking on three pieces of fruit a day and to do nothing else for four weeks. 

V-L: Why is fibre so important for gut health? Is one type of fibre better than another? 

AD: So we used to think that the only function that fibre had in the human body was to help us to not be constipated. We used to think that the large bowel and the colon only had two functions: absorbing water so we don't get dehydrated and making poop to get rid of waste. That's all we thought it was good for. But we now understand that fibre is really important for our overall health. 

It's really interesting because when you look at the big studies, you see that the number one dietary predictor of poor health outcomes is low fibre consumption. So people who eat insufficient fibre are at increased risk of heart disease, obesity, type two diabetes, Crohn's disease, heart disease and diverticular disease. All of these conditions fill up our hospitals and GP waiting rooms in countries where we now eat a standard Western fibre-deficient diet. 

The diversity of fibre within our diet is the number one determinant of a healthy gut microbiome. And of course, one of the other things that's so wonderful about fibre is that we get it from whole plant foods. High fibre intake tends to be a great marker of the fact that you are eating plenty of fruits, vegetables, whole grains, legumes, nuts, beans and seeds. All of these foods are consistently shown to benefit human health. 

The soluble versus insoluble fibre debate is a little bit artificial. I think the world of fibre is actually incredibly complicated. I've read entire in-depth publications in the medical literature debating what sorts of fibre we have and I wonder whether the terms soluble and insoluble even mean anything of note.

What's really important is how our digestive system treats these various foods and fibres. But in broad terms, we think of insoluble fibre as being the scrubbing brush that's the kale in your smoothie that helps to move things through and prevent you from becoming constipated. And then we think of the soluble fibre as the fibre that dissolves in liquid. So we get a lot of soluble fibre from foods like kiwi fruits. But in practice, all plants contain various levels of soluble and insoluble fibre. So it's quite difficult to tease them out. It's a slightly artificial approach to nutrition, but they're both important. 

V-L: The gut is sometimes referred to as the second brain. Can you explain why that is? 

AD: I guess what people are alluding to is the gut-brain axis. So our digestive health and our neurological health seem to be very tightly linked. We've seen so many studies showing that healthier dietary intakes help to promote happiness: which is what everybody wants. And I wrote about this in my book - The Plant-Based Diet Revolution - I call it the happiness effect. We see this all the time. 

I've worked with thousands of people and supported them in making the transition to a healthy, whole food plant-based diet. Whatever their initial motivation was, whether it was for their digestive health, their overall health, or whether they're doing it for the environment or animals, when you check back in with people about four to six weeks after they've embarked on a whole food, plant-based diet, and you ask them how they're doing, the word that they use is happy. They will say things like, I feel lighter. I feel happier. I'm being nicer to people is what one nationally renowned chef told me when he switched to a whole food plant-based diet. There are lots of reasons for that. 

Of course, it could be that eating in an evidence-based way that reduces our risk of chronic disease and reduces our impact on the environment, and knowing that we're doing that may make us happy. So it's hard to tease that out. But also by eating a diet that's higher in complex carbohydrates may actually help our body to boost its levels of serotonin, the happy hormone. We also know that a healthy whole food plant-based diet contains fewer proinflammatory molecules and chronic inflammation is very tightly linked to depression, poor mood and poor energy levels, etc. 

There are some very interesting studies looking more directly at manipulation of the gut-brain axis, but sadly, almost all of those studies have been done in animal subjects and we don't have a tonne of research yet in humans, although there have been some tantalising results, for example, feeding people certain probiotic cocktails. So these are cocktails of active bacteria that take up residence in our digestive system and you can actually detect changes in the brain on functional MRI, which is a really vivid representation of how important what goes into our system is for our neurological health. 

Another example of how our gut and our brain are connected is when you eat a healthy whole food plant-based diet with a diversity of fibre, your digestive system is optimised for the production of these chemicals called short-chain fatty acids, which are efficiently made by fibre-loving bacteria. 

Short-chain fatty acids have so many beneficial effects on the human body that it's hard to keep up with the literature. They help control our blood sugars, our appetite, maintain the integrity of our gut epithelial barrier and help control so many aspects of human health, reducing chronic inflammation. There's one short-chain fatty acid called butyrate, which after it's made by our gut microbes, is absorbed into our bloodstream, passes through our entire body, enters our cerebral spinal fluid, travels to our brain and helps to maintain the integrity of the brain blood barrier. The brain-blood barrier is a complex system within the human body that helps to keep toxins out of our brain. So our gut microbes are making medicine that helps keep our brain healthy. Phenomenal.

Dr Alan Desmond

V-L: The full title of your aforementioned book is The Plant-Based Diet Revolution: 28 days to a happier gut and a healthier you. Can significant progress be made in a space of a month towards improving gut health?

AD: Absolutely. When you make the changes to your diet, the beneficial effects begin to manifest within days. There is a research paper in Nature which is aptly named ‘Diet rapidly and reproducibly alters the human gut microbiome’ which highlights that within 28 days - or perhaps as little as 14 days - you will see remarkable changes in the structure and function of your gut microbiome such as significant increases in the production of short-chain fatty acids; reduction in the production of the harmful postbiotics from your gut microbes; your gut mucosa will become healthier; your metabolism will start to adapt; and that's just when it comes to the gut health perspective. 

A few years ago, I ran The Southwest Plant-Based Diet Challenge which put about 150 health professionals on a healthy, whole food plant-based diet for 28 days and we saw an average weight loss of about 5 kg, which is important because a significant number of the volunteers were overweight or obese. 

We saw a drop in high blood pressure of 14 mercury, which is the equivalent of going on one or two antihypertensive medications. And we saw LDL cholesterol (often called ‘bad cholesterol’) drop by about 25%.

V-L: What are your plans over the coming years to continue to champion plant-based nutrition? 

AD: What I'd really like to do is build on the previous challenges that I've done with healthcare professionals and continue to get the word out there to healthcare professionals. So I'm still actively engaged with speaking at medical conferences, running events to engage GPS hospital doctors, NHS administrators, etc. to get the message out to them, because people forget. In the last few years, healthcare professionals have done a lot for people: the pandemic times have been really challenging for healthcare professionals.

Often healthcare professionals neglect their own health rates of chronic disease: depression, obesity, heart disease, etc. are relatively high in our doctors, nurses and other healthcare professionals. So I want to get these folks, my colleagues and coworkers throughout the UK, to experience these health benefits for themselves, to learn how to cook the food themselves, and then they will be better equipped to give evidence-based dietary advice to their patients.

That sounds like a great plan Dr Alan, thank you for all you are doing in raising awareness of the benefits of a whole food plant-based diet. If you are interested in learning about more ways a plant-based diet could aid your wellbeing check out our articles: can a plant-based diet help prevent and treat type 2 diabetes? or can a plant-based diet help keep Crohn’s disease in remission?