Modern-day eating has become a minefield, says award-winning food journalist Hattie Ellis in her new book, What to Eat? 10 chewy questions about food.

Hattie Ellis navigates modern food conundrums, simplifying the landscape of how to eat well and with a conscience, and successfully sorts the wheat from the chaff (at one point quite literally when she explores flour milling and bread), interviewing foodies from farmers to bloggers and bringing together a career’s worth of research to demystify food for us.

With 10 themed chapters ranging from best breakfasts to local food, Hattie Ellis explains how to eat both healthily and responsibly, without losing the joy of eating. Is red meat good for you? What about no-carbs diets? How can “green” cooking and sustainable eating be made cheaper and easier? Concluding each chapter are clear action points for changing your approach to sourcing, cooking and eating food.

The well known phrase “an apple a day keeps the doctor away” was originally a marketing slogan used by American apple growers at the beginning of the 20th Century, wrote Hattie Ellis. Their fruit had been made into cider, but after the drink was banned during Prohibition they tried to promote apples as being good to eat instead.

So how true is that old adage?

Apples have taken a bashing lately for being full of sugar, which dentists warn causes tooth decay, but advising against them is like throwing the baby out with the bathwater. Apples are a good source of fibre. There are two types – the first is insoluble, also referred to as roughage, which increases the bulk of stools, and in turn stimulates gut contractions and keeps the bowels moving regularly.

The second type, soluble fibre – which apples contain – dissolves in the stomach, forming a viscous gel. It helps food move along the gut too by adding bulk, but it also lowers cholesterol by binding to it in the gut. This gel slows down the rate at which sugar enters the bloodstream, keeping energy levels steady.

The Department of Health recommends that adults consume 18 g of fibre per day, and a medium apple provides about 3 g – similar to a bowl of brown rice. Several studies into the cholesterol-lowering properties of apples recommend eating two a day to get a beneficial dose.

By hitting the daily recommended fibre intake, we may be lowering our risk of colorectal cancer. While diets containing more than 80 g of meat per day have been linked to a higher incidence of these tumors, a fibre-rich diet seems to cancel out this effect. The peel, which contains insoluble fibre, has the highest concentration of disease-fighting flavonoids and polyphenols, although this research is based on concentrated extracts rather than the whole fruit.

As for vitamins, variety matters. A single old-fashioned Ribston Pippin has more Vitamin C than a whole pound of Golden Delicious.

You can drink some of the goodness in an apple as well as eating it. Juicing doesn’t alter the vitamin content dramatically, although you do lose a lot of the fibre. Cider vinegar has long been used as a folk-medicine tonic. Science has shown that it can lower blood-sugar levels and that it helps with weight loss, probably by suppressing appetite.

A 2009 Japanese study showed drinking a 500 ml drink with a tablespoonful or half-tablespoon of cider vinegar led to greater weight loss, because people ate less, and lower blood cholesterol than drinking water. Mix a splash with honey and oil to make a healthy salad dressing.

What is the best breakfast?

Packaged cereals shout about nutritional goodness. But a recent survey by the consumer organization which showed 32 out of 50 types were shockingly high in sugar. This is the type of refined sugar dentists are right to be concerned about. And, it can be argued, these cereals won’t keep us full until lunch.

Sugary breakfast cereals have a high glycaemic index (GI) score – a measure of the effects of carbohydrates in food on blood-sugar levels. It estimates how much each gram of digestible carbohydrate in a food raises blood glucose following consumption, relative to consumption of glucose. GI scores are calculated in relation to glucose, which has the highest score of 100.

The higher a GI reading, the faster the food is digested and the quicker we are hungry again. Conversely, the lower the GI, the longer we feel full and the fewer calories we consume.

This is the reason why a low GI diet is associated with healthy weight, and a lower risk of type 2 diabetes and heart disease, according to the University of Sydney’s International GI Group.

Cornflakes, which are some of the least sugary cereals, have a GI score of more than 80, which is similar to white bread. Low-GI breakfast foods include muesli (avoid added-sugar varieties) and porridge.

“Go to work on an egg” – another old marketing phrase – is good advice. Eggs contain protein which makes you feel fuller for longer. A poached egg on wholegrain toast is a great choice.

A full English fried breakfast contains protein and fat as well as carbohydrate – and will keep you full for a long time. However, the calories can be alarmingly high, so a regular fried breakfast will only make you put on weight. As for bread, sourdough has a higher acidity than others due to the addition of lactbacillus, which produces lactic acid, giving it a distinctive tangy taste. There is ongoing research into how this element aids absorption of nutrients such as calcium, zinc and iron better than standard bread.

A glass of freshly squeezed juice is a refreshing shot of vitamins. The British Dietetic Association recommends a small (150 ml) glass. Best of all, have the fruit whole or eat some chopped up with live natural yogurt.

Can I eat to avoid heart disease and cancer?

No one food will kill or cure. But the good news is that a balanced, varied diet has room for fats and carbs – just choose the right kind in the right amounts. Fats help build our cells and are part of good health, but they are high in calories. Eating too many calories can lead to you becoming overweight, which raises risks of heart disease and cancer. Butter has been demonized in the past, but like other fats it delivers and contains fat-soluble vitamins such as A, D and E.

Wholegrains are another key food.

“They provide fibre and micronutrients such as folic acid, magnesium and Vitamin E,” says Professor Walter Willett of Harvard Medical School, where researchers have shown how a diet rich in grains is associated with lower rates of cancer and heart disease. Oatcakes, porridge, wholegrain couscous, brown rice and quinoa are good options.

The World Cancer Research Fund recommends having no more than 500 g of cooked red meat in a week due to the risk of colon cancer. A slice of roast beef is 45 g, a thick piece of lamb 90 g and a small steak is 100 g.

Moderate wine-drinking is championed by Professor Roger Corder, at Barts and the London School of Medicine. In his book The Wine Diet, he recommends traditionally made red wines, which are high in polyphenols, especially one type, procyanadins. These seem to be particularly good for cardiovascular health by protecting against the damage to your blood vessels that causes disease. Such wines range from those from Madiran in south-west France (look for the Tannat grape) to the Douro in Portugal.

The word “superfood” refers to those that are rich in phytochemicals, the micronutrients in food other than vitamins and minerals that protect your body against disease. Tomatoes, onions, garlic, cabbage and green tea are also rich in these compounds and are affordable.

How should I eat my five a day?

Fruit and vegetables contain vitamins, minerals, phytochemicals and fibre and they are low in calories. But only a third of adults eat their five a day. Five turns out to be a number created by the State Nutritionist for California in 1998. She looked at the average figure of what people ate and doubled it.

A 2011 study in the European Heart Journal showed that people who ate eight a day were 22% less at risk of dying of heart disease than those who ate three a day.

It’s good to eat vegetables in abundance because they are very high in micronutrients and have less sugar than fruit. Eat as many different kinds as possible and try to “eat a rainbow”, as the pigments are linked to different phytochemicals.

A number of micronutrients, including Vitamin C, are best consumed raw or steamed, rather than boiled, in order to not destroy the more fragile types and lose water-soluble vitamins in cooking water.

But fat-soluble vitamins such as A, D, E and K can be more useful when cooked in a little fat. The antioxidant lycopene in tomatoes is better absorbed this way.