Less meat, more plants

The simplest way to reduce your personal carbon footprint is to go vegan. Growing beef takes as much as 100 times more land than growing peas or soya to produce the same amount of protein. I’ve reduced my meat consumption to some local, organic grass-fed red meat or a roast chicken as an occasional treat once or twice a month. This allows me to enjoy meat as part of my diet at a more sustainable level.

Studies have demonstrated no differences in gut health between vegans, vegetarians and occasional meat-eaters. The single most important dietary factor we found for better gut health was the number of different plants we eat weekly, with 30 a week being the optimal number.

That might sound like a lot until you realise that this also includes mushrooms, spices, nuts, seeds, herbs and legumes. Simply using a sofrito base of onions, garlic, olive oil and carrots when cooking, and adding some mixed beans or lentils to your pasta sauce or a spice mix to your cooking, or sprinkling mixed nuts and seeds on your yoghurt, can rapidly boost this number.

Ditch ultra-processed meat alternatives

Unfortunately, many vegans over-rely on high-salt and fatty ultra-processed foods that are bad for us and the environment (some produced in large, energy-intensive factories). Newer production methods, such as cell-cultured “meat”, “fish” and even “cheese” are on the horizon, and are likely to be more environmentally friendly.

Brands like Symplicity (currently stocking restaurants nationwide and soon to be available to consumers) use large scale vats to ferment organic vegetables with no artificial additives, making “meatballs” and “burgers” that benefit our gut microbiome and with near zero waste.

Choose pulses over animal protein

We worry too much about protein. It’s pulses, beans and lentils that help centenarian populations in some cultures outlive the rest of us. This is due to their high-fibre, protein, mineral and polyphenol content (polyphenols are the plant chemicals that help our gut microbes).

We need iron and iodine, zinc and vitamin B-12 to be healthy, but most of us can easily absorb these from eggs, clams or mussels and chicken – the most sustainable farmed animal products – once a week.

In 2017, I visited the Hadza people in Tanzania and measurably improved my gut microbiome diversity in just three days by eating all the plants and seeds, fruits and nuts that they eat in one week – along with the odd porcupine.

Go organic, even just a little

Herbicides were generally considered safe before we realised the importance of microbes, both to the soil and our guts and immune systems. Our own data has shown the power of a healthy diet and microbiome to protect against severe disease.

Pesticides and herbicides are designed to disrupt natural ecosystems, reducing biodiversity and degrading our soils, impacting our water life and the survival of insects. We ingest these chemicals in small amounts every day and they are hard to avoid, especially with plant-based diets.

While it’s beneficial to only buy organic foods where possible, the current level of organic farming is insufficient to produce enough food for us all. And that’s not to mention the difference in price. Buy local and seasonal ingredients that stay fresher for longer. It’s worth prioritising certain foods: I always buy organic strawberries, oats, spinach and apples as non-organic varieties tend to have the highest levels of herbicides.

Cook smarter (and use the microwave)

We can reduce cooking-fuel consumption and preserve the beneficial chemicals in food by harnessing the power of microbes to ferment and preserve leftover vegetables.

Kimchi, for example, uses cabbage, green veg, garlic and chillies, while heating food in a microwave saves energy while generally maintaining the nutrient content. I now microwave a whole potato instead of baking it, and steam spinach in the microwave too. I make vegetable soups, ferment leftover vegetables (such as sauerkraut or beetroot), eat the hard outer leaves of cauliflower, and freeze softening fruits.

Fish has been overhyped

The science on fish has changed, and it is now clear that the health benefits of fish and omega-3 fats have been overrated. Studies of omega-3 supplements show no clinical benefit unless you’re pregnant or have had a recent heart attack, and fish is less beneficial for the heart than we thought. Plus most fish we now eat in the UK, including salmon and trout, come from non-sustainable aquatic farms.

Use a local fishmonger or supermarket fish counter you trust and can ask questions. Mussels and clams are healthy, largely sustainable and very tasty.

The dairy dilemma

Dairy is a massive cause of global heating, and its health benefits, such as strengthening bones, have been overplayed. There are plenty of better sources of calcium, for example, sesame seeds and tahini, dark-green leafy vegetables and calcium-set tofu. Although dairy alternatives are better overall for greenhouse emissions, they can cause other problems; the excessive amount of water used to create almond milk and its harmfulness to bees, for example. Others, such as soya and oat milks, can be highly processed.

Personally, the only milk I haven’t given up is fermented milk, known as kefir, which I make myself and have a little shot of every day for my gut microbiome.

Make it personal

The fact is, there is no one diet that suits us all. But the rapidly emerging field of personalised nutrition (led by companies including ZOE, which I co-founded) suggests that, by predicting which foods best suit our body, we can reduce sugar and fat peaks in our blood and improve our gut health. We can feel better, have more energy and feel less hungry – all without discussing calories.

But as we wait for technology including apps, at-home tests and continuous glucose monitors to help us eat more healthily, we can make positive changes by following the broad approaches described here. Meanwhile, listen to your body and eat more of what makes you feel good.

Give yourself a break

Nobody’s perfect, and the enjoyment of food, and the social interaction that comes with it, can be as important as environmental and health considerations. Even small positive changes can go a long way.

• This article was amended on 30 October 2022 to remove a reference to “improving calcium intake” among the “overplayed” benefits of drinking milk.

Food for Life by Tim Spector is published by Vintage (£20). To support the Guardian, order your copy for £17.40 at guardianbookshop.com. Join the waiting list for the ZOE app at joinzoe.com