You’re eating all day long

One of the challenges with the sheer availability of food in today’s world is that lots of us end up spending many of our waking hours eating. Whether it’s full meals, snacks or desserts, scientists have found that it’s not uncommon for us to be mindlessly grazing at some point during all of our 16 or so waking hours.

The problem? As soon as this food hits the bloodstream in the form of glucose, it initiates the release of the hormone insulin. This in turn activates a switch present in every one of our cells, which is responsible for driving cell growth and proliferation.

We need this mechanism to survive, but too much cell proliferation can be a bad thing. It leads to more random mutations in your DNA and, over time, a greater likelihood of cancer, as well as fuelling the growth of a damaging form of internal fat known as visceral fat.

As Eric Verdin, president and CEO of the Buck Institute for Research on Aging in Novato, California, points out, our bodies need time away from eating to have a chance to focus on repair. He says: “There is a lot of evidence for this – 12 hours fasting and repairing, and 12 hours eating and building is more conducive to healthy ageing.”

You’re eating too many refined carbs …

You may not have heard of advanced glycation end products, or AGEs, but these toxins are responsible for pretty much every aspect of the ageing process that we’re familiar with, including wrinkles, stiffness, cataracts, loss of heart elasticity and even Alzheimer’s disease.

AGEs are formed during a chemical process called glycation, where sugars in the body react with proteins or fats. They’re best known for turning collagen – the protein that gives our skin its youthful elasticity – into a drier, stiffer form. “AGEs change protein structure and, at the same time, cause a large amount of inflammation,” says Jaime Uribarri, a kidney doctor at the Icahn School of Medicine at Mount Sinai in New York, and one of the world’s leading experts on AGEs.

Glycation happens more often when there’s an excess of sugar in the bloodstream, which occurs when we eat sweets containing a rapidly absorbed simple sugar called fructose or easily digestible refined carbohydrates such as white rice, white pasta and pizza dough.

… and cooking at too high temperatures

AGEs can also be created within foods – particularly those containing a lot of protein and fat, such as meat, cheese and fish – when they are grilled, barbecued or fried at high temperatures. Researchers such as Uribarri are concerned about the long-term health impacts of eating lots of bacon, for example, as one of his studies found that just three slices of bacon fried for five minutes contain 91,577 AGEs, compared to just 23 AGEs in a tomato.

To limit the accumulation of AGEs in our bodies, it’s recommended to eat more whole grains such as brown rice, while Uribarri suggests trying to do more slow-cooking and stewing rather than grilling.

You’re aggravating your immune system with too much saturated fat (and not enough fibre)

Saturated fat – mostly found in animal products such as red meat, cheese and ice-cream – is broken down into ceramides. These have been shown to be capable of reprogramming immune cells in the gut into a more inflammatory state. This can lead to the gut wall becoming more leaky or permeable, making it more likely that microbes and toxic metabolites could leach into the bloodstream. Over time, this can accelerate the ageing of the immune system.

The good news? Scientists have found that our guts can handle a certain amount of saturated fat, as long as we’re also consuming sufficient amounts of fibre and omega-3s, for example from oily fish. These foods actively help to resolve gut inflammation.

“We’ve found that two of the biggest dietary features associated with immune ageing are higher consumption of saturated fat and lower consumption of fibre,” says Niharika Duggal, an assistant professor in the University of Birmingham’s department of inflammation and ageing. Scientists specialising in ageing say we should be consuming the equivalent of 1g of omega-3s per day – which could be achieved by eating one mackerel fillet or two to three salmon fillets once a week – as well as at least 40g of fibre (present in whole grains and legumes).

You’re not getting enough B vitamins

If you’re interested in wellness, you’ve likely come across NAD+, a molecule that plays a critical role in how our cells generate and manage energy. While there’s now a vast industry based around NAD+ supplements, our bodies make it naturally when we consume vitamin B3, found in foods such as turkey, tuna and anchovies.

This is just one example of the importance of optimising your intake of B vitamins to age well. The body uses them to make chemicals called methyl donors, which give it the ability to turn certain genes on or off at the right times. For example, ensuring that certain key tumour suppressor genes are kept turned on, defending us against cancer. Without sufficient methyl donors, this process becomes less well controlled as we age.

Not getting enough vitamin B12, which is found in foods such as salmon, tuna, beef, eggs and dairy products, can also make you more likely to develop a leaky gut, and even precipitate memory loss and slower brain processing speeds. This is one of the reasons why, if you’re over 50 and experiencing signs of cognitive decline, it’s particularly important to ensure you’re not deficient in vitamin B12.

Your diet is too acidic

We all need a certain amount of protein in our diet, but balance is everything. In recent years, epidemiologists have become increasingly concerned that too many people are getting a high dietary acid load from their food.

This is essentially because we tend to consume a lot of protein, added salt and phosphoric acid (a common preservative and flavour enhancer in ultra-processed foods), which the body metabolises into acidic substances. However, we tend not to eat sufficient dietary potassium – which we can get from various fruits, vegetables and dried herbs (the drying process helps concentrate the minerals present) – to counterbalance all these acids.

This places increasing stress on the kidneys, the body’s main acidity regulator, and over many years this has been linked with a variety of chronic health conditions. “As your kidneys fail, your ability to get rid of these acids goes down, so the problem gets progressively worse,” says Lynda Frassetto, a kidney specialist and a professor at the University of California, San Francisco.

Ageing researchers advise us to focus on eating twice as much fruit and vegetables as protein with each meal.

You’re consuming too few healthy fats

There’s a very good argument to suggest that omega-3s – found in oily fish and available as relatively low-cost supplements – are one of the most potent anti-ageing tools of all.

As well as helping resolve gut inflammation caused by saturated fat, they are involved in numerous health-promoting functions around our body, from maintaining brain and heart health to retuning the immune system. They’re even involved in regulating muscle mass across the course of your life. Ageing science has shown that getting enough omega-3s can prevent an age-related condition called anabolic resistance, which impairs our body’s ability to build new muscle fibres from dietary protein, accelerating the onset of frailty.

While consuming the equivalent of 1g of omega-3s per day has been linked with slowing biological ageing, most of us don’t come close to getting enough.

You’re missing out on immune-stimulating phytochemicals

Alzheimer’s Research UK has previously highlighted studies showing that people who consume more phytochemicals – found in brightly coloured fruits and vegetables – are at a lower risk of cognitive decline.

Take passion fruit, for example. Two years ago, I attended a conference where Norwegian ageing scientists presented data suggesting that regularly consuming these fruits may be protective against brain ageing. Similar discoveries have been made relating to pomegranates, strawberries, grapefruit, tomatoes and various teas.

But why? Ageing experts believe that when our bodies metabolise these fruits, they may rev up the brain’s immune cells, prompting them to work more efficiently to clear toxins and promote repair.

You’re eating too much at night

Finally, think about when you tend to eat your biggest meal of the day. If that’s dinner – as is the case for most people – you may want to try switching to a bigger breakfast or lunch and a smaller evening meal, at least some of the time.

When we eat big meals at night, it’s not only more disruptive for our sleep – a vital time for our body to carry out important repair – but we’re also consuming a large number of calories at a time when our metabolism is at its most sluggish.

“Our insulin sensitivity is much better in the first half of the day,” says Satchin Panda, a professor at the Salk Institute in San Diego, California. “This allows us to manage [the blood sugar rise after eating a meal] much better.”

So what should I eat?

Dr Cox’s perfect longevity menu

This menu is low calorie and nutrient dense. It concentrates the protein-heavy meals in the first half of the day, when your metabolism is at its most efficient. It contains two portions of leafy greens, which are rich in vitamin K and also important for minimising dietary acid load. The lunchtime mackerel will provide a heavy dose of omega-3s, and the walnut snack will provide other micronutrients. Finally, it contains 40-50g of fibre, which will help nourish your gut and immune system.

Breakfast
Egg, spinach and mushroom muffins (or you could try these savoury muffins)

Lunch
Smoked mackerel salad (try Nigel Slater’s version)

Dinner
Chickpea, spinach and coconut curry with brown rice, served with cauliflower (Check out Rukmini Iyer’s twist)

Snack
1 medium pear with 3 tbsp walnut halves. Two cups of green tea

The Age Code by David Cox is published by HarperCollins at £22. To support the Guardian, order your copy at guardianbookshop.com. Delivery charges may apply