Diet experts slam Robert Downey Jr's new health book for spreading 'harmful misinformation' - like telling readers to eat TREE BARK

Cool Food was co-written by Robert Downey Jr and journalist Thomas Kostigen. The book released in January

Dietitians have slammed a new book by Oscar winner Robert Downey Jr, which claims that $6 sugary water from  diluted maple syrup is as healthy as tap water, suggests potatoes spike our blood sugar like candy - and advises swapping lettuce for a hunk of tree bark.

The book, written in collaboration with environmental journalist Thomas Kostigenfor, contains 'harmful misinformation' that could lead readers to avoid perfectly nutritious food, the nutrition experts have warned, leading to potential health harms.

Some of the advice is also said to be only applicable to the 'very privileged', as lauded produce like tree bark costs around $14 for an eight-ounce bag. 

In one chapter, the actor recommends opting for 'better' green vegetables like kale, alfalfa sprouts and bok choy. 

Dr Carolyn Williams, registered dietitian and author of Meals that Heal, told DailyMail.com that advice like this is 'harmful misinformation'.

'This sort of thing makes me mad - and it's a very privileged way of looking at food.

'There are lots of people who aren't eating any healthy foods at all, like greens and vegetables. The last thing they need is a list of ingredients that are a) expensive and also that many people have probably never heard of.

'We want people to eat any leafy greens to improve their health - there aren't specific ones that are better than others.'

Robert Downey Jr has long been considered a climate activist and philanthropist, now writing a climate and diet book with journalist Thomas Kostigen

The criticisms of the actor's latest endeavor come after he was awarded the Best Supporting Actor Academy Award for his role in Christopher Nolan's atomic bomb thriller, Oppenheimer.

When accepting his award, Downey Jr, 58, said that making the movie had made him a 'better man'.  

Cool Food, which was published in January, provides 'practical steps to reduce our carbon footprint.' It does this mostly by suggesting a host of lifestyle changes including reducing car and air travel and avoiding running applicances like dishwashers. 

But the majority of the recommendations revolve around food and diet. Eating meat has also been shown to increase these gases by as much as 25 times. 

However, experts say the authors are 'ill-equipped' to offer nutrition advice as it appears that a dietitian did not vet the recommendations.

'They should have stayed in the sustainability lane,' said Dr Williams.

'The authors are assuming that if something is sustainable and has a lower carbon footprint, it's healthier. And that's not necessarily the case.' 

Cool Food's co-author, Thomas Kostigen, is a climate journalist and New York Times selling author. He is not a medical professional

One section of the book compares nutritional advice from Harvard University with Government recommendations made by the US Department of Agriculture. 

The authors include a quote from Harvard's advice that states: 'Potatoes are chock full of rapidly digested starch, and they have the same effect on blood sugar as refined grains and sweets, so limited consumption is recommended.' 

While potatoes do have a high glycemic index, meaning that they lead to blood sugar spikes, experts said comparing the effects on the body to sweets is an 'unfair comparison'.

'Potatoes are chock full of nutrients, and actually, they do not raise blood sugar the same, immediate way as foods like sugar-sweetened beverages and white rice,' Michelle Routhenstein, New York-based registered dietitian told DailyMail.com.

'It's not the same thing. It's not a fair assessment.'

Ms Routhenstein said that this generalization could lead people to cut out the potatoes entirely, which are rich in vital nutrients like vitamin C, fiber, and potassium. 

The authors of Cool Food also dive into expensive trends. For instance, one recommended product is maple water, which costs around $6 for a bottle, and is made from taking the sap from maple trees and diluting it.  

The authors write: 'Maple's health benefits are also plentiful. It has fewer calories than honey and is high in nutrients like riboflavin, zinc, magnesium, calcium, and potassium, according to nutritionists.' 

Riboflavin, also known as vitamin B12, helps oxygen-rich red blood cells form, while zinc supports immune and metabolic health. 

Magnesium and calcium are key nutrients in building bone and muscle health, while potassium helps maintain fluid levels in cells.

'We're offering you a proverbial - and in some cases literal - menu to think abut, research more, or talk about with other people,' Downey Jr (left, with Oppenheimer co-stars Emily Blunt and Cillian Murphy) writes in the introduction

A 12-pack of 33.8 fl oz Drink Simple cans, for example, costs $77. Each bottle has 2.5 servings and comes out to 30 calories per serving

According to the Cleveland Clinic, maple water does contains antioxidants like manganese, which has been shown to reduce muscle inflammation, and fight oxidative stress in the body. 

However, Dr Williams noted that the amount of these compounds in maple water is likely to be exceedingly low.  'I'm sure maple syrup has trace amounts of these things, but I don't know if it has that much,' she said.

What's more, Dr Williams points out that maple water contains excess calories and sugar. For instance, a 33 fl oz serving of one popular brand, Drink Simple, contains 7g of sugar (more than you'll find in a Chips Ahoy! cookie) and 30 calories.

Maple water brands also claim they boost hydration with electrolytes. However, a 2019 study found that neither maple water nor coconut water were more hydrating after a workout than regular water. 

'I don't think this drink is going to hydrate you better than other waters,' Dr Williams said. 

The authors also suggest embracing your inner survivalist and eating tree bark. 

Though tree bark is rich in fiber, experts warned that there are better ways to get the key nutrient

'Seaweed can be nutrient-dense and a source of certain vitamins and minerals, but I don't necessarily think it's a great idea to do this at home,' Dr Williams said

'Elm bark and pine bark are touted as especially good,' they write. They also recommend birch, spruce, fir, and tamarack.

'Bark extracts are also a thing, especially pine bark extract,' they write. 'They are used as herbal supplements for use as an antioxidant, antimicrobial, and anti-inflammatory, among other purposes.'

'We aren't suggesting that we all turn into Bear Grylls. But there is something to be said for using every part of the tree, especially if it means the tree can keep standing.' 

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Navigating the ever-expanding selection of milk and dairy alternatives can leave your head spinning. 

Dr Williams said that bark is loaded with fiber, which slows gastric emptying, the process in which food moves from the stomach through the digestive tract. This keeps you full for longer and can help prevent bowel cancer.

However, there are plenty of other foods out there packed with fiber that probably taste better and are cheaper, she said. These include oats, avocados, raspberries, broccoli, and whole grains.

Additionally, an eight-ounce bag of bark from Naturejam Encinom for example, costs $14, whereas an entire head of broccoli costs about $2.  

'The nutrients in tree bark aren't going to be any more nutritious than eating another good fiber source,' Dr Williams said. 'If you're in a truly survival mode and you have nothing to eat, it might come in handy, but it seems kind of crazy.'

Dr Williams also called attention a section in the book titled 'Better Leafy Greens than Others. It listed okra, kale, bok choy, red cabbage, spinach, watercress, and alfalfa sprouts.

'Leafy greens aren't going to differ that much,' she said. 'Basically, we just need to get more leafy greens. They're all beneficial.'

It's unclear if the designation of 'better' means that these picks are more sustainable or more nutritious, but Dr Williams warned that this vagueness could lead to people assuming that certain greens are better than others. 

'That is not the case. And even the suggestion is harmful.'

DailyMail.com contacted the book's publishers Blackstone publishing for comment, but the company declined.