Brain Power: Everything You Need to Know for a Healthy, Happy Brain

By Catherine de Lange

An essential guide to living better for longer, Brain Power breaks down the science behind brain function and reveals why sleep, exercise, diet and even socializing are so important for our health.

What does it mean to have a healthy, happy brain, and why is it so important to look after our grey matter? Comprehensive and illuminating, this is an essential and up-to-date examination of how lifestyle choices impact our ability to maintain a healthy brain.

Focusing on important areas such as diet, sleep, exercise, brain training and emotions, Brain Power explains the science behind what really affects our brains, as well as providing practical tips and exercises to improve and support brain function into old age.

• Language: English
• Publisher: Michael O'Mara
• Release date: Jan 6, 2022
• ISBN: 9781789293456

Catherine de Lange

Catherine de Lange is a science journalist, editor and author of 10 Voyages Through the Human Mind: Christmas Lectures from the Royal Institution published by Michael O'Mara Books. She has written for Nature, the Guardian and the Washington Post among others, and has worked on TV programmes such as the Royal Institution Christmas Lectures, as well as radio documentaries including BBC Radio 4's Dear Professor Hawking. She is currently Editor of New Scientist.

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PART 1

DIET

The brain is a hungry organ, consuming about 20 per cent of the body’s energy. And yet, when we choose what to eat, we are more likely to be thinking about the effects on our physical health. Is it good for the heart? Will it make me put on weight? Does it cause cancer or diabetes? It’s not just individuals who think this way: by and large the medical profession too has underappreciated the role that diet plays in our mental wellbeing. That is despite the fact that we have long known that the gut is not a standalone organ, and that it is in constant dialogue with the brain. Now, science is starting to home in on this conversation, and the findings are quite astounding.

One way that the gut and brain communicate is through the microbiome, on which there has been an explosion of research in recent years. In Chapter 1, we get acquainted with the trillions of microbes living within us, and discover the incredible ways they influence our wellbeing. Crucially, we will also learn how to feed them to keep them – and by default, ourselves – happy.

In Chapter 2, we go on to explore the idea that it isn’t just what we eat, but also when, that plays a role in staying sharp. Fasting diets of all types are growing in popularity, but are they all they are cracked up to be, and can going hungry really fine-tune your brain?

Bad diet is the leading risk factor for death in the majority of countries around the world, claiming more lives than smoking.⁴ Where have we gone wrong? In Chapter 3, we take a tour of some of the global hotspots that have the healthiest diets, and learn from them and the latest research about what we should actually be eating for optimal brain health and a long and healthy life.

Finally, if you still aren’t convinced about the role of diet on the brain, in Chapter 4 we turn to what happens when our body’s ability to cope with food breaks down, and to the striking idea that Alzheimer’s disease could be a kind of diabetes of the brain.

Throughout this part of the book, we will discover the antidote to the multitude of diets and fads that promise a quick fix, and instead learn the sustainable, delicious changes that we can make to our diets to keep our brains fighting fit.

CHAPTER 1

What to eat to boost your mood

Butterflies in your stomach on a first date, a gut feeling that someone isn’t being honest with you, even a tummy upset in anticipation of a big work presentation: we have all experienced the connection between the gut and the brain in some form. But did you know that the gut has its own nervous system? Or that the gut is in constant dialogue with the brain, influencing your thoughts and moods even when you aren’t eating? This connection is so strong that scientists have come to call the gut our second brain, and are gleaning a better understanding than ever of how we can all nurture this connection to feel and think better.

The two-way communication between the gut and the brain is called the gut–brain axis, and information can travel back and forth in a number of ways. The most direct is the vagus nerve, an information super-highway that sends signals from our gut to our central nervous system, and is a key player in the body’s ‘rest and digest’ mode. The vagus nerve is considered to be the body’s sixth sense,⁵ because of its ability to detect activity in our organs and communicate that important information back to the brain. Aside from the vagus nerve, the gut can talk to the brain in other ways, including through hormones, the immune system and through our gut microbes.

Our understanding of the influence of the gut–brain axis on our mental health is relatively new, especially the role of the microbes that live in our gut. Even so, it’s an extremely exciting area of research, with compelling evidence that the way we treat these residents of our intestines can have a profound influence.

Meet your microbiome

We have an estimated 40 trillion microorganisms living in our digestive tract. To put this into perspective, this is about the same number as cells that make up the human body, and there are 100,000 times more microbes in your gut than there are people on the Earth.⁶

They predominantly make their home in the large intestine, the final part of the digestive tract, and the slowest part of the digestive system, taking about twelve to thirty hours to process what’s coming through, giving plenty of time for our gut microbes to work their magic. These trillions of microbes, which include bacteria, viruses, fungi and parasites, are together called our microbiota. In combination they house hundreds of times more genes than your own genome – all the genetic material in your own body. It is this collection of microbial genes that we call the microbiome.

Remarkably, until the twenty-first century, 80 per cent of the microbes in our guts were a mystery to us. That’s changing thanks to gene-sequencing technology, and in 2007 the Human Microbiome Project was launched to sequence our ‘second genome’. We are now entering an exciting phase, where the focus is shifting from what these inhabitants are, to what they are getting up to in there – and how we can make the most of them to influence our physical and mental health.⁷

We often hear talk of ‘good bacteria’, and this is a key concept when we think about our gut microbiota. Our digestive tract is one of the prime ways that harmful organisms can enter the body. If we have enough ‘good’ bacteria in there, any unwanted pathogens will be outnumbered, helping to protect us from infection. This is one reason why, when it comes to health, it’s important to have as diverse a microbiome as possible. The more skills it can perform, the more it can do to keep us well.

But our gut residents do much more than simply outcompete harmful microbes. They also break down foods that are indigestible to us, producing a number of useful compounds, or metabolites, and make vitamins, including all eight B vitamins. Remarkably, our gut microbes can also produce neurotransmitters, the chemicals our brain cells use to communicate, including serotonin (a lack of which is implicated in depression), noradrenaline (which primes the body for action) and dopamine (which plays a vital role in mood, and in our ability to learn and plan). In fact, 50 per cent of our dopamine is made in the gut.⁸

Powerful influencers

All of this goes to show that our gut microbes are not merely passengers hitching a ride inside us. Their health is tightly connected to our own, and they can exert a powerful influence over our brain.

Just how big that influence is has started to become clear through research over the past decade or so, starting with studies in germ-free mice. These are mice that are bred without any microbes and raised in a sterile environment, allowing scientists to see what effect exposure to various microbes has on them. Pioneering research in 2004 by a team of Japanese researchers found that these microbiome-free mice had underdeveloped brains, an exaggerated stress response, and seemed to act as though they were depressed.⁹ Tellingly, after the mice were fed a mix of bacteria, their stress response quickly became normal.

Further compelling evidence comes from studies using faecal transplants, during which faecal material from one individual is transferred to the gut of another, often through an enema or sometimes orally, for instance in pill form. One review of this technique, published in 2020, looked at studies of faecal transplants into mice from people with specific conditions. After the mice received the transplant, they developed symptoms similar to those seen in humans – including depression, anxiety, anorexia and alcoholism. Of course, these symptoms aren’t exactly the same as in people, but are a proxy – for instance, mice displaying anxiety will spend less time in the middle of an open field, preferring to stick to the edges. Those displaying compulsive behaviours will frantically bury marbles, given the chance. Simply transferring the microbiome of someone who is poorly into these mice seemed to also transfer the health issue.

What if we could do the opposite, and transfer the microbiome of healthy individuals into those with pre-existing health conditions, in an attempt to get rid of them? It’s a tantalizing idea, and while few studies have taken place in people, a handful do exist. For instance, the review identified six studies where feacal transplants took place from healthy volunteers to people with depression, and all of the studies found short-term improvements in depressive symptoms in those receiving the transplants. However, the symptoms generally returned to previous levels after several months.

ANTIBIOTICS AND THE MICROBIOME

On the whole, antibiotics seem to be bad news for your microbiome, messing with the balance of microbes in your gut (of course they are also an incredibly important treatment for bacterial infections, so you should still follow doctor’s orders where needed). However, the picture is complicated by evidence suggesting that activity of antibiotics on the microbiome might also help people with persistent negative symptoms of schizophrenia or those with depression who are resistant to standard treatments. So the role of antibiotics on the microbiome – in both the treatment and prevention of disease – is likely to become a hot topic in the years to come.

As for how these effects take place, it could be through any of the number of ways the gut talks to the brain. Neurotransmitters and short-chain fatty acids, produced when gut microbes chew up fibre from our diet that we can’t digest ourselves, can both fire up the vagus nerve, sending signals to the brain. Indeed, when mice have their vagus nerve cut, the beneficial effects of gut microbes disappear.

Short-chain fatty acids are also anti-inflammatory and can influence the immune system in other ways too. Given that many psychiatric illnesses are influenced by inflammation (see Chapter 25 for more on this), the anti-inflammatory powers of the gut microbiome are particularly intriguing.

The psychobiotic revolution

Faecal transplants are still an extreme option and in 2020 the US Food and Drug Administration (FDA) issued a warning over the risk of serious infections related to the practice.¹⁰ An alternative suggestion is that we might give people probiotics – bacteria that have proven health benefits for the gut – as a way to treat mental-health problems, an idea that leading researchers John Cryan and Ted Dinan at University College Cork in Ireland and their colleagues coined ‘psychobiotics’.

But how sure can we be that effects of the microbiome we see in animals apply to humans? One piece of evidence starts with a tragedy in 2000 in the Canadian town of Walkerton, Ontario, when heavy rains caused the water supply to become infected with E. coli and campylobacter from cattle excrement. It resulted in an epidemic of bacterial dysentery, which infected half of the population and tragically killed seven. Many of the survivors went on to develop post-infectious irritable bowel syndrome. But, says Dinan, a significant proportion of patients developed major depressive illness by the end of the first year, suggesting that the pathogen somehow managed to impact on their brains.¹¹ Research also shows that people with depression, PTSD and schizophrenia have striking similarities in their microbiome that they do not share with matched controls.

Adding to the idea that our gut microbes influence our emotions, investigations of healthy women using brain scans have shown that the levels of certain bacteria in their guts influences the way they respond to emotional pictures – so much so that researchers could use the brain images to predict which kind of gut bacteria the women had. This was pretty convincing evidence that these gut-residents can influence our emotional responses.¹²

The team responsible for these findings, from the University of California, Los Angeles, went on to show that giving women a probiotic yogurt containing bacteria twice a day for four weeks improved the way their brains processed emotions. In clinical populations – that is to say, those already with a mental-health condition – probiotics might also help. In some studies, the approach has been found to reduce symptoms of depression and anxiety.¹³

Before you head off to stock up on probiotic yogurt, hold fire. There are plenty of products on sale that claim all sorts of benefits to our health, but even Dinan says that the majority of probiotics his group have tested in the lab yielded no effect on the mind, and there’s no guarantee that the bacteria ingested will survive the journey through your stomach acid to reach the large intestine. To make matters worse, not only are we in the dark about which bacteria are going to be truly effective in boosting mood, but each of us also has a different gut microbiota, so the likelihood is that what works for one will not work for all. Until we figure all this out, the promise of psychobiotics remains just a promise for now.

Take care of your microbes

It seems clear that protecting the trillions of helpful microbes living within our guts and keeping them healthy can also help to protect our mental health.

But how do we best do that? According to the gut-health doctor Megan Rossi, at King’s College London, the most important thing is to eat a diverse range of plant-based foods, in order to nurture a diverse microbiome. She says that due to modern agricultural techniques, the diversity of our plant food sources has plummeted, with 75 per cent of the world’s food generated from just twelve plant species.¹⁴ So the challenge is on to eat as wide a variety of plants as possible – she recommends at least thirty different plant-based foods a week. This might sound daunting, but with a few tricks up your sleeve (see the box below) they add up fast. While you’re at it, make sure you include plenty of fibre, which can’t be broken down by our digestive systems but feeds our microbiome, and is then split into those all-important short-chain fatty acids that are so good for us. They also seem to help regulate stress and anxiety.¹⁵

SIMPLE WAYS TO EAT BETTER FOR YOUR MICROBIOME

•Eat mainly plants and try to get in at least thirty different varieties of plant-based foods a week. This includes fruit and vegetables, pulses, nuts and seeds. Fibre, especially wholegrain, is particularly good.

•Avoid too much refined and heavily processed food, and sugary food and drinks.

•Herbs and spices are an easy way to add variety to your diet, and pack it full of flavour too.

•If you have access to a weekly fruit-and-veg-box delivery, it can be a fun way to increase the diversity of the food you normally eat.

•Sprinkle mixed nuts and seeds on top of cereal, yogurt or soup – each variety counts towards your weekly thirty.

•The same goes for mixed salad leaves – an easy way to diversify your diet with minimal effort.

•Freeze excess fruit and vegetables to retain most of the nutrients, and pop them into smoothies or other dishes.

Other than diet, there are several things we can also do to help look after our microbiota. One of those is to get enough sleep. Your gut microbiome has its own circadian rhythm, with its activity following a twenty-four-hour cycle, so disrupted sleep can mess with it too. And getting more sleep helps us to make healthier food decisions – a win-win for the microbiome. (See Part 2 of this book for tips on getting better sleep.)

Stress can make the gut leakier, allowing bacteria into the bloodstream. This can trigger inflammation, too much of which is bad for both physical and mental health. Cryan and his colleagues have done research in mice that shows that the short-chain fatty acids that are released by gut microbes after we eat fibre can help repair some of this damage – another reason to get that fruit and veg into your diet.

All in all, the evidence is mounting that the gut influences our moods and vice versa. When we feed ourselves to feel good, we should consider what our gut microbes like to eat too – keeping them onside is likely to become an increasingly important way to bolster our physical and mental health.

CHAPTER 2

Going hungry could keep your brain young

If you are a diehard breakfast fan, this chapter might be hard to swallow. I’m a firm believer that breakfast tastes so great because we’ve usually not eaten for a good ten or more hours beforehand. But what if you could hold off a little longer? The impact on your brain might be worth the effort.

Neurogenesis – the growth of new brain cells – has been linked to increased cognition and better mood, but unfortunately it naturally decreases with age. In fact, until relatively recently, the ability to grow new brain cells was considered to be exclusive to the young, with adults stuck with those they acquired in childhood and their teenage years. Happily, evidence is now stacking up that adults too can grow brain cells in some areas, including the hippocampus, well into old age, and as a result, any strategy that gives rise to these new cells is good news (see Chapter 16 for more on neurogenesis). One approach that’s garnered a lot of attention is calorie restriction, otherwise known as fasting.

Hungry worms

The practice of fasting has long been a part of religious and cultural traditions, and the scientific community is catching on. All kinds of organisms, from yeast to worms and mice, live longer (as much as 80 per cent longer in the case of rats) when put on a highly calorie-restricted diet, generally one that sees them cutting out around 40 per cent of their daily calories.

Dieting in this way seems to be particularly beneficial for the brain, in other animals at least. Mice that were given a rodent-version of Alzheimer’s disease, for instance, and who then ate 30 per cent fewer calories for four months, had improvements in markers of the disease on the brain. As long as vitamins, minerals and other essential nutrients are coming in, mice on a calorie-restricted diet have been found to have increased brain plasticity and better function of synapses, the connections between brain cells that play a vital role in learning and memory.¹⁶ And mice put on a long-term calorie-restricted diet also had improvements in their working memory, which you can think of as the ability to hold numerous pieces of information in your mind while you do something else – a skill that decreases markedly as the brain ages.

Why might eating less be good for us? As our cells break down the food we eat, they release rogue compounds called free radicals that can damage other cells and tissues and contribute to the ageing process. So one theory on the benefits of fasting is that eating less gives our metabolism a break, affording our body respite from this process.

Miserable lifestyle

The potential of calorie restriction as a route to a longer, healthier life has led some determined individuals to give it a go, strictly limiting the amount they eat day in day out. For most us, however, consistently eating so few calories would leave us feeling miserable and hungry, and possibly questioning the appeal of living longer in such a state of mind.

Recently, however, scientists realized there could be a simpler way to achieve the effects of fasting without the perpetual hunger. They noticed that when animals are put on a calorie-restricted diet in experiments, they tend to simply be given their food in a smaller window, and eat nothing at all the rest of the time, rather than being allowed to eat a smaller amount throughout the day. And there is a growing consensus that it is this switching between fasting and eating normally again that makes calorie-controlled diets so good for the body and brain. Indeed, studies looking specifically at intermittent fasting protocols, where animals are allowed to feed during a small allotted time window, have shown promising results, including for obesity, diabetes, cardiovascular disease, cancers and neurodegenerative diseases.

FASTING AND BRAIN DISORDERS

In the next few years, it will be interesting to see whether fasting can help with symptoms of brain disorders such as Alzheimer’s disease, Parkinson’s and stroke. Animal studies certainly look promising, not least because ketones that are produced when we fast and used by the body for fuel have been shown to stimulate the production of a molecule called BDNF, which is important for learning and memory, and the ability of the brain to adapt to stress, as well as in helping the brain to protect itself against disease. Furthermore, fasting rodents that have Alzheimer’s-like brains do better on learning and memory tasks. Fasting has even been shown to reduce damage in the brains of animals that have been given something akin to a stroke. One of the reasons ketones might be a promising area of examination for Alzheimer’s disease is that the brains of people with the disorder have a reduced ability to use glucose, possibly because the transport of glucose is blocked by amyloid plaques that build up in the brains of people with Alzheimer’s. So, switching to a different energy source could be beneficial to maintaining brain function.

The thinking is now that, rather than passively reducing free radicals produced from digestion, intermittent fasting puts the body into a kind of repair