When Eva Humphries first started working as a nutritionist, she met a client who had just found out he had high blood pressure and high cholesterol, and was on the verge of type 2 diabetes. He had no idea how to change his diet or lifestyle.

The man broke down and cried for 45 minutes, leaving Humphries with “no idea of what to do”, she says. In the final 15 minutes of the session, scrambling for a quick but helpful message, she finally said: “When you look at a plate of food, can you just make half of it veg for me?”

The client came back two months later and “the colour was back in his cheeks”, she says. He told her that adding the veg had “started to [make him] feel really good”.

It’s a simple approach to eating more plants – and one we might all need to start emulating, sooner rather than later. Earlier this month, a new report found that, due to deteriorating soil quality, crops including carrots, apples and peas are now 20% to 50% less nutritious than they were in the 1960s. So should we be eating double the amount?

When I was a child, the “five a day” mantra for fruit and veg was drummed into me and, as an adult, I thought I was doing OK. I’m vegetarian, which means that most of my meals revolve around plant-based foods; I subscribe to a vegetable delivery service from a local community farm; and I frequently snack on apples. I actually do eat my five a day, most of the time – and often exceed that.

But even before these findings, there was research suggesting we should aim for 10 portions of fruit and veg per day, instead of five, while some experts advocate for consuming 30 different plants a week. Eating – and affordably sourcing – that kind of volume can feel overwhelming, and the news about declining nutritional value is potentially demotivating.

William Summers, senior associate at Deep Science Ventures, which published the new report alongside charity the Mark Leonard Trust, hopes the findings make farmers and policymakers consider and prioritise nutrient density. In the meantime, he doesn’t want people to imagine that there is no point in eating plants. His research has shown that “whole foods, across cereals, fruit and veg, have definitely got less nutrient dense. That’s a fact – but they’re still way, way better than eating ultra-processed foods.

“There are certain vegetables that are known to be more nutrient dense and that’s tied to their genetics,” he adds. “Broadly, it’s leafy greens. So I’d say the more leafy greens you can get in your diet, the better.”

According to last year’s National Diet and Nutrition Survey, only 17% of UK adults get their five a day, which can include, fruit, vegetables, beans and pulses. So how can we consume more plants without really trying?

A first step could be switching out meat for beans in meals you already make. Dr Shireen Kassam, visiting professor of plant-based nutrition at the University of Winchester, and executive director of Plant-Based Health Professionals UK, suggests swapping a tofu curry for a chicken curry, or a lentil bolognese for one made with mince. Even if you don’t want to lose the meat completely, a “half and half” meat and lentil bolognese is a good way to sneak in vegetables without entirely changing the flavour, she says.

Matt Beardmore, executive chef at the Italian restaurant Legare, also uses pasta sauces to pack in veg. At his restaurant, the focus is on taste, but at home, to get the maximum nutrition, he will double or triple the amount of sofrito (an onion, celery and carrot base for sauces) that he normally puts into a recipe. As the weather gets colder, Kassam and Beardmore both recommend soups as a way to use up any sad-looking leftovers in your vegetable drawer. With a soup such as minestrone, “you can just absolutely fill it with veg”, Beardmore says.

His rule of thumb is “filling half my plate with veg” – which is what Humphries suggests, too. The approach she used with the unhappy client at the start of her career has become a guiding principle for the way she now works. “It’s this concept of: if we look at a plate visually, can we just shove a couple more pieces of veg on it, or maybe add some herbs or a handful of greens? I think we underestimate how far little practices like adding an extra portion of vegetables can go.”

The next step, says Humphries, is to diversify your intake, to ensure you’re consuming as many different minerals and vitamins as possible. “We tend to get into a repertoire of eating broccoli and peppers and peas,” she says. One question she challenges her clients with is “when was the last time you’ve had watercress? Or, when was the last time you added a handful of fresh parsley on top of your food?” Fresh herbs are quite concentrated sources of nutrients, she says, so you don’t need to eat a lot to receive benefits. The idea is to get people thinking about easy ways to add new vegetables and other plants to the diet they already have.

One plant we could be eating more in the UK is seaweed, says Humphries, particularly because it contains iodine, one of the minerals flagged by Deep Science Ventures as having been lost from our soils. “It’s got loads of iodine, iron, calcium and magnesium,” she says. “It’s one of those other plant foods that we don’t often think about.” You also don’t need a lot of seaweed in your diet to reap the benefits, so eating a bit of sushi, which often features a dried version called nori, will give you your fill. “I typically tend to use it in seasonings because it’s got quite a salty flavour,” says Humphries.

The way we cook fruit and vegetables matters, too. “Typically, vitamins C and B tend to go from vegetables if you boil them,” says Humphries. “C is broken down by heat, and then a lot of the B-vitamins leach into the water.” On the other hand, certain vegetables actually improve when boiled: “Say, for example, iron in spinach. We can barely absorb any iron from raw spinach, but we can absorb it really well when it’s cooked or boiled”.

Neither Humphries nor Kassam recommend getting over-worried about cooking methods, though – increasing your quantity of vegetables is the main thing. “For most people, the basic message remains the same: five a day is the minimum,” says Kassam. If you can manage more, that will serve your body well.

To maximise the nutrients you absorb from the food you already eat, choose wholegrain varieties wherever you can – thereby “reducing the reliance on refined grains and going for brown rice, brown pasta”, Kassam says. One surprising thing that Kassam and Humphries tell me is that soaking beans and pulses before you cook them can also increase their bioavailability – which helps you to absorb more nutrients from them.

Beans might be a great source of selenium and zinc, but it can be hard work for us to actually absorb those minerals if they haven’t been soaked for a long period or cooked very slowly, Humphries explains. This is because beans contain phytates, which are “anti-nutrients, and their main job is to bind minerals”, she says. “So when we eat beans or grains, we can’t fully absorb those minerals because they’re bound to these phytates. So the only way that we can get around it is to do things like soaking beans overnight. Because that tricks the plant into thinking that it’s about to sprout, and it releases the phytates.”

This is great news if you’ve got the time and capacity to think ahead and prep your beans in advance – but the reality is that most of us buy beans in cans or jars. Most ready-to-eat beans in cans will have been boiled quickly, Humphries says – so while eating them is still good for you, you’re not maximising their nutritional content that way. For a convenient alternative, Humphries recommends the Bold Bean Co, which sells pre-soaked and slow-cooked beans in jars – but these are approximately four times the price of supermarket own-branded cans.

The most nutritious option does often come with a cost, says Humphries, who says that she can’t afford to eat 100% organic produce, even though she would like to. Does choosing organic actually make a nutritional difference? “Our data on organic isn’t particularly brilliant,” she says. But she wants people to be aware that “when we metabolise pesticides or any kind of artificial chemicals that are left on our food, we use nutrients to detox it” – so there is actually a case for pesticide-free produce allowing us to retain more nutrients.

If you can afford to buy organic and local, that’s great, says Humphries, “because we know that having a farmer down the road who really cares about supporting their local community is ultimately supporting more than nutritional wellbeing – it’s supporting our local economy. We also know that, when things are picked, they start losing nutrients fairly rapidly. So having access to fresher produce does have merit.”

For this reason, if you are able to grow your own fruit, vegetables and herbs in your garden or on your windowsill, you are likely to catch more of the plants’ nutrients before they start degrading. That is probably “the one advantage”, nutrition-wise, that has been proven when it comes to homegrown v shop bought, according to Summers. “There isn’t a huge body of evidence, but from what there is, there doesn’t appear to be any reliable differences” other than “simply freshness”, he says. “The sooner you either eat or preserve it, the better.”

“Ultimately, as a nutritionist, my heart lies with: ‘get the vegetables in’” – in whatever way is affordable and manageable – says Humphries. While Kassam would recommend switching sugary snacks for fruits, nuts and crudités (the third one to pack in even more vegetables outside meals), “ultimately we have to recognise that unhealthy calories are cheaper than healthy calories”, she says. She points to the charity the Food Foundation’s most recent Broken Plate report, which showed that a fifth of UK households would need to spend 85% of their income on food to afford the government-recommended healthy diet, and that the price gap between healthier and less healthy food is now the widest it has been in over a decade.

Because of this, Kassam says, “people don’t always make active choices: their choices are made in the food environment, what’s affordable, what’s familiar. We need to be representing healthier options in our supermarkets and incentivising those purchases.”

There are ways to maximise your plant consumption slightly more cheaply: frozen vegetables still count, and sometimes even contain more nutrients than fresh ones. “There are cases where rapidly freezing veg will give better nutritional quality than fresh veg that has been sat around long enough to have time to degrade,” says Summers.

“I tend to stash three to four different types of vegetables in my freezer,” Humphries says, so she’s always got a handful of spinach or peas to add to her meals.

If you have room, keeping a store cupboard full of “tins of beans and wholegrains and things that are always going to make a nutritious meal” is also a good, and relatively cheap, way to ensure that you always have plant foods on hand, even if you haven’t got anything fresh in, says Kassam.

But, she adds, any increase in fruit and vegetable intake is beneficial. “We’re not talking about being perfect.”