Why meal replacement drinks like Huel aren’t as healthy as you might think

Ten years ago, the Silicon Valley software engineer Rob Rhinehart wanted to free himself from the hassle of preparing food. He did some research, bought 35 chemical compounds he deemed vital for survival, blended them together and lived off the gloop for three months, refining the formula as he progressed.

He named the product Soylent after the 1973 dystopian sci-fi film Soylent Green, in which people are fed food made from human remains.

This food hack idea caught on. Increasingly, people are reaching for products such as Huel replacement drinks, German-based yfood, Nu26, Protein Works meal replacement shakes and the Dr Micheal Mosley-backed Fast 800, whose shake powder promises convenience and nutrition based on a Mediterranean-style diet.

According to Mordor Intelligence, the meal replacement market is worth $2.12 billion in Europe in 2024 and expected to reach $3.16 billion by 2029. Anyone who spends time in motorway services and eats on the go will understand why. Food courts can resemble nutritional deserts full of high-calorie, high-fat junk food.  

But it all begs the question, can a salted caramel shake, like those peddled by Huel, really replicate the nutritional benefits of fresh grilled sardines and a Greek salad drizzled in extra virgin olive oil?

The short answer is no. But when the options are no food, or junk food, could meal replacements present a better option?

What are the drawbacks of meal replacement shakes?

Kyle Crowley, the strategic projects director at Protein Works, is upfront about the limitations.

“Meal replacement shakes are not designed to replace ideal meals,” he says. “In an ideal world, we would all be eating ideal meals around the clock. Unfortunately, however, most of us don’t have the time, or the budget to do this, at least not every day. If you have the time and budget to make a salad with mixed greens, lean protein, extra virgin olive oil, nuts and pomegranate seeds, please do. Do it as often as you can,” he says.

If not, Protein Works meal replacement shake, which includes thiamine, vitamin A, vitamin B12, vitamin B6, vitamin C, vitamin D, zinc and iron, claims to provide over 150 health benefits which include reducing tiredness and fatigue, supporting muscle function, bones and teeth health, and boosting immunity. These benefits relate to the macronutrients, vitamins and minerals included in the product, and are the legal claims which can be made about those ingredients under the European Commission Food and Feed Information Portal. 

Huel prefers to position itself as an alternative meal, rather than a replacement. James Collier, Huel’s co-founder and its chief sustainable nutrition officer is a registered nutritionist and former NHS dietician. He explains: “People refer to these things as replacements because they are not ‘normal food’, but what is normal food?”

What is Huel? 

Huel is described as an “on-the-go, powdered, plant-based food, providing all 26 essential vitamins and minerals, protein, essential fats, carbohydrate, fibre, and phytonutrients”.

Collier claims that Huel is a “complete” food that contains “a proportionate amount of all the essential nutrients”, adding: “We make nutritionally complete, convenient, affordable food with minimal impact on animals and the environment.” 

The British company produces a range of products including ready-to-drink shakes, powders, bars, and instant meal pots. 

Are meal replacement drinks actually good for you?

Dr Adam Collins, an associate professor of nutrition at the University of Surrey, says that the common profile of a meal replacement includes fats and fibre, high-protein, vitamins, minerals and other nutrients which may include prebiotics and probiotics.

“They are formulated to meet a perceived ideal nutritional profile, so from that perspective they are good,” he says. “The reality, however, is that the nutrition is provided as a powder or a drink in a blended form, so there is no solid food matrix involved.”

In other words, the nutrients in meal replacements do not necessarily interact with the body in the same way that intact food does. The comparison would be similar to the difference between eating an apple and drinking an apple that has been pulverised in a blender. Nutrients may be absorbed at different rates in different parts of the digestive system. Collins says this is not necessarily a negative, and likens the effect to taking multivitamin supplements, which do not always confer the same benefits as consuming the same vitamin or mineral in a food.

In 2022, Huel funded a peer-reviewed study published in the journal Frontiers of Nutrition in which 20 subjects lived off a 100 per cent Huel diet for four weeks. During that time, 22 key blood markers were monitored along with BMI and other body measurements. At the end of the trial, 14 of the parameters significantly changed. Haemoglobin, iron, vitamins B12 and D and selenium significantly increased. Blood glucose, total and non-HDL (bad) cholesterol, vitamins A and E, potassium, BMI, visceral adipose tissue (a metabolic form of fat), and waist circumference all significantly decreased.

A 2014 study published in the journal Hormone and Metabolic Research compared the effects of solid meal-replacement products with liquid meal-replacement products of similar energy content on hunger, satiety, and appetite-regulating hormones in older adults. The study concluded that people who drank liquid meal replacements became hungrier quicker than those who ate solid versions. It concluded that meal replacement drinks should not be viewed as a dietary equivalent to a solid.

What is the controversy over meal replacement drinks?

Meal replacement foods are heavily processed and made from processed ingredients. With the current focus on the dangers of ultra-processed foods (UPFs), manufacturers are taking pains to distance their products from this market sector.

Collier from Huel maintains that not all processed foods are bad.

“There is this whole thing that all UPFs are bad at the moment,” he says. “There is a lot of push back in academia about that because there are a lot of things that we need to address, such the fibre shortage in diets and sustainability, and products like Huel are addressing these.”

Many people who use meal replacement products report gastrointestinal discomfort, and particularly flatulence. This is due to some of the ingredients used. High protein content, whey, fibre, artificial sweeteners, and emulsifiers can all cause gut problems. Often it takes the stomach time to adjust to a new diet.

In the United States, Soylent was criticised for the levels of lead and cadmium in its products which were below US safety levels but above the levels permitted in California without additional labelling. In 2016 the company also recalled its snack bars after reports they caused nausea, vomiting, and diarrhoea. 

Do you lose weight on these types of drinks?

 Apart from Slim Fast, meal replacements are not specifically marketed as weight loss products although some people do use them in calorie-controlled diets.

They can be beneficial as part of a weight loss programme because they contain a standardised number of calories, so consumers know exactly how much is in each product.  But they are not low-calorie products. They are designed to contain the same number of calories as a light meal, typically between 350 and 400 calories. Indeed, consumers who use them as a snack, rather than to replace a full meal, may find they gain weight.

What effect can meal replacement drinks have on the gut?

Jordan Haworth, a clinical physiologist at The Functional Gut Clinic in London, explains that consuming meal replacement products occasionally is unlikely to cause any changes to the gut microbiota, the gut microbiome, and the gut flora. Collectively these are the microorganisms, including bacteria, fungi, and viruses, that live in the digestive tracts and which are vital to overall health. However, consumers should be mindful of some of the ingredients and claims made.

“Some of them have around six grams of fibre, which is OK but you would expect to get more from a meal,” says Haworth. “And if they have artificial sweeteners such as sucralose or aspartame, that may cause changes to the gut microbiota if you are consuming them every day.”

Natural sweeteners like stevia are less likely to have a negative effect. Products which contain whey or casein can also cause issues with people who have a lactose intolerance. Protein Works Diet Meal Replacement Extreme, for example, contains milk protein concentrate, micellar casein and sodium caseinate (the company also makes vegan versions of the product). Meanwhile yfoods chocolate flavour classic powder includes milk protein and both yfoods and some Huel products include sucralose.

Many products also contain probiotics, or friendly bacteria, which are thought to be beneficial to gut health. However, these are in dried-form, and not live cultures that you would find in products like kefir and kombucha. More studies are needed to assess how beneficial these dried powders are.

“The main message is, don’t replace a whole meal [with meal replacement drinks] where you get more fibre and more polyphenols, which are anti-inflammatory plant compounds,” concludes Haworth.

What are the negatives?

Kate Hilton, a clinical dietician at Feel Gut and Diets Debunked, says: “If you are intolerant to certain carbohydrates known as FODMAPs (fermentable oligosaccharides, disaccharides, monosaccharides and polyols), you may find you experience increased gas, bloating, pain and diarrhoea.”

FODMAPs include compounds such as lactose, fructans, sugar alcohols and galacto-oligosaccharides.

“Ingredients to look out for include different fibre types like chicory, or sweeteners like sorbitol, mannitol or erythritol,” continues Hilton. “The fortification of these foods may be a little too much for some people with particularly sensitive guts. Magnesium, in particular, has been known to cause a stomach upset in some people, and so could contribute to symptoms.” 

It is also advisable to look out for certain sweeteners in products. Nestlé’s Optifast meal replacement shakes, for example, contain aspartame. A 2021 analysis of previous studies into the controversial compound was published in the journal Nutrients. It highlighted a list of worrying possible side effects including headache, convulsions and depression. 

It stated: “Some studies suggest that aspartame consumption has influence on obesity levels, glucose and insulin intolerance, and changes in the microbiota of the offspring of rats. In humans, there have been reports of premature birth as well as allergic reactions and weight gain in the newborns. Studies involving girls aged nine to 10 have shown that aspartame increases the risk of an early first menstruation. Aspartame consumption can cause mood disorders, mental stress, and depression. Maternal absorption of aspartame during pregnancy correlates with autism in children.”

Meanwhile a 2021 study published in Advances in Nutrition fund that sucralose may alter bacterial metabolism in the body, with possible consequences for cholesterol metabolism and an increase in inflammation, although a randomised controlled trial of 34 participants given sucralose capsules for seven days found there was no significant change in their gut microbiota. 

Why are some meal replacements high in fat?

 Not all fats are equal. Saturated fats can be unhealthy and are found in butter, cream and fatty meat, while mono and polyunsaturated fats can be beneficial and are found in olives, sunflower oil, walnuts, flax seeds and oily fish.

Most of the calories contained in meal replacements come in the form of fats, which include monounsaturated, polyunsaturated and saturated, most however are low in saturated fat. The fat in Huel ready-to-drink, for example, provides 42 per cent of the total energy and is made up from rapeseed oil, flaxseed and sunflower lecithin. These are essential fatty acids and are rich in monounsaturated omega-3s and omega-6s.

Is it OK to have these types of drinks every day?

Probably not. While they are formulated to meet recommended nutrition guidelines, and in some cases exceed those recommendations, they often lack vital components provided through regular healthy food. So while occasional consumption is unlikely to cause problems, habitual use could have long term complications. 

Collins says: “They are not a bad thing. They are not a panacea either. They have a time and place and are useful as a meal replacement for people on the go, not as an additional thing you can have sin-free.”

Hilton says there is not enough research into the long-term effects of replacing several meals a day with meal replacements but that it could be detrimental to health.

She says: “Ultimately, they are fine to have on occasion as a meal replacement, however I wouldn’t recommend for people to have more than one per day. Whilst they do provide the macro and micronutrients we need in a meal, they don’t yet provide all of the non-nutritive compounds, such as anthocyanins and polyphenols that we would typically see within whole foods.”

Not all meal replacement shakes are created equal, says Hilton. “Huel, for example, has more fibre than SlimFast. In low-fibre diets we can assume that low-fibre shakes affect gut microbiome and reduce the amount of good bacteria in the gut. That can cause long term issues, such as increasing the risk of colorectal cancer.” 

Hilton believes we don’t have the evidence to make a direct link, but that low-fibre diets lead to an increase of these types of conditions. “Even those products with high fibre generally only include fibre from a limited number of sources, so there is not going to be as much bacterial diversity as there would be if someone was eating real food,” she continues. 

Having a variety of sources of fibre can encourage a healthier gut microbiome, she says. “An adverse impact on gut microbiome diversity may have an adverse impact on health further down the line.

“If you don’t have a strong gut microbiome, for example, your gut won’t be producing a compound called buterate, which is an anti-inflammatory chemical which can reduce the risk of cardiovascular disease and type 2 diabetes.” All food – liquid or solid – for thought.