If you’ve ever tried losing weight with meal replacement shakes, you might wonder: can a powder or bar really match the benefits of real food? A groundbreaking new study published this week suggests the answer is no – real, whole foods may deliver superior results for both weight loss and health. You don’t need to sacrifice convenience for quality, either.

Researchers from Deakin University’s Food & Mood Centre conducted a single-blind randomised controlled trial comparing two Very Low Energy Diet (VLED) programs: one using traditional supplement-based shakes and bars, and one using whole foods (specifically, pre-packaged meals from Be Fit Food).

The results are outstanding and have big implications for anyone looking to shed pounds in a healthy way.

A closer look at the study design

To set the stage, let’s explain what they did. In this trial, 47 women (ages 30–65) with obesity were randomly assigned to one of two diet plans for three weeks:

• Whole-Food VLED: Participants ate Be Fit Food meals, which consisted of about 800–900 calories per day of mostly real, minimally processed ingredients (around 93% whole foods). These meals included a variety of vegetables, legumes, lean proteins, dairy, nuts, seeds, herbs, and spices – basically a nutrient-dense, real-food diet but in a very low-calorie format.
• Supplement-Based VLED: Participants followed a typical meal-replacement program of shakes, soups, bars, and dessert sachets providing the same ~800–900 calories per day. However, about 70% of the ingredients were industrial or highly processed – things like protein isolates, emulsifiers, artificial sweeteners, thickeners, and other additives found in many commercial shake-based diets.

Importantly, both diets were designed to have the same calorie count and similar macronutrient breakdown (protein, carbs, fat). This way, any differences in outcomes could be attributed to food format and quality (whole-foods vs. processed replacements) rather than differences in calorie intake.

The trial was “single-blind,” meaning the outcome assessors didn’t know which diet each participant was on when measuring results, to reduce bias. By the end of the three weeks, both groups had lost a similar amount of total weight – confirming that severe calorie restriction (a hallmark of VLEDs) does lead to weight loss.

But here’s the twist: despite equal calories and pounds lost, the whole-food diet group showed remarkable health advantages over the shake diet group.

Key findings: whole food diets deliver superior results

The researchers measured a variety of outcomes – from body composition to gut health markers and metabolic hormones. Here are the key findings that stood out, in plain language:

More fat loss, less muscle loss

Even though total weight loss was similar, the whole-food group lost significantly more body fat and better preserved their lean muscle mass compared to the supplement group. In other words, the quality of weight loss differed. The shake-based dieters tended to lose more lean tissue (muscle) along with fat, whereas those eating real foods primarily shed fat while hanging onto muscle. Preserving muscle is crucial – it keeps your metabolism revved and supports long-term weight maintenance – so this is a big win for the whole-food approach. Higher protein quality and nutrient diversity in the real food meals may have helped protect muscle even during rapid weight loss.

Healthier gut microbiome

The gut microbiome – the trillions of bacteria in our digestive tract – changed very differently between the two groups. The whole-food diet dramatically boosted gut diversity (the variety of beneficial bacteria), while the meal-replacement diet did not. In fact, microbial diversity increased by about 40% in the whole-food group but decreased slightly in the shakes group. Researchers use diversity as a key indicator of gut and overall health, linking more diverse gut bacteria to improved digestion, immunity, and even mood.

The whole-food VLED group also ended up with a greater number of beneficial bacteria species (particularly fibre-loving species associated with veggie intake) and a more stable gut ecosystem overall. By contrast, those on the all-shakes diet saw a drop in some helpful microbes and greater disruption in the balance of their gut flora.

This finding makes sense: real foods (like veggies, nuts, and legumes) are rich in fibre and plant compounds that “feed” good gut bacteria, whereas ultra-processed shakes often contain additives (emulsifiers, artificial sweeteners, etc.) that can harm the microbiome.

The study is actually the first of its kind to show that even under strict calorie restrictions, the format of food matters – whole foods can preserve a resilient gut microbiome, while heavily processed meal replacements may upset it.

Improved metabolic flexibility

The whole-food group didn’t just have happier gut bugs – they also showed signs of a metabolically healthier state. In particular, they experienced improvements in metabolic flexibility, which is the body’s ability to switch efficiently between burning carbohydrates and burning fats as fuel.

One clue was seen in a hormone called leptin (which helps regulate hunger and metabolism). Leptin levels became more stable as gut diversity improved in the whole-food group, indicating the body was adapting better to the low-calorie intake rather than “panicking” metabolically.

Essentially, the real-food diet appeared to help the body remain balanced and switch energy sources smoothly, whereas the processed diet might make one’s metabolism more rigid or stressed. Better metabolic flexibility is associated with sustained energy, less hunger, and easier weight management after a diet.

Fewer side effects and better overall well-being

Participants eating real foods generally felt better on the diet than those on shakes. According to the study, the shake group reported more than twice as many side effects (like headaches, bloating, and constipation) compared to the whole-food group.

By contrast, those on the whole-food program had fewer digestive complaints and even saw improvements in bowel regularity (likely thanks to the higher fibre content and absence of artificial sweeteners or other irritants in the real food meals).

Anyone who’s tried a meal replacement diet knows that issues like constipation can be common – this research suggests a whole-food VLED is gentler on the body while still delivering results.

Why Does Food Format Matter So Much?

At first glance, weight loss is often portrayed as simply “calories in vs calories out.” This study reinforces that quality matters just as much as quantity. When you drastically cut calories, what you’re eating can shape how your body responds:

Muscle Preservation

Whole foods (like lean meats, dairy, and legumes) provide not just protein but a matrix of nutrients – amino acids, vitamins, and minerals – that likely help maintain muscle tissue during weight loss. Highly processed shakes might have protein too, but they lack the complexity of real food. It appears that getting protein in a natural form, along with fibre and micronutrients, helps signal the body to hold onto muscle and burn fat instead.

This aligns with prior knowledge that higher protein diets with quality nutrients support lean mass during dieting, but here it was achieved with real food rather than powders.

Gut health links

Our gut microbiome thrives on natural plant fibres and diverse foods. When we switch to only processed meal replacements, we may starve certain gut bacteria or introduce additives that disrupt the gut environment.

A healthier gut (as seen in the whole-food group) can reduce inflammation, improve nutrient absorption, and even influence hormones that regulate weight. This trial demonstrated that even equal calories led to opposite effects on gut health depending on food processing.

In the long run, a nourished microbiome might help guard against weight regain (since some gut microbes can influence how we store fat or how hungry we feel). Real food essentially “partners” with your gut bacteria, while processed shakes can inadvertently work against them.

Metabolic signals

Real foods typically lead to steadier blood sugar and insulin responses compared to sugary shakes or artificial ingredients. The observed stabilisation of leptin in the whole-food group suggests their bodies weren’t “shocked” by the diet as much as the shake group. The whole foods might better communicate satiety and nutritional sufficiency to the body.

Metabolic flexibility is crucial because if your body can smoothly shift to burning fat for fuel, you’re likely to feel more energetic on a diet and rebound less afterward. The whole-food diet’s positive effect on metabolic hormones hints that it sets the stage for more sustainable weight control beyond the diet period.

Big picture: real food for weight loss – a new gold standard?

This study is being hailed as a groundbreaking milestone in nutrition science. It was published in the high-impact journal Cell Reports Medicine (Cell Press)—a testament to the quality and importance of the research. What the findings essentially confirm is something many experts long suspected: for effective and healthy weight loss, real whole foods should be the preferred approach over ultra-processed “diet” products.

Yes, you can lose weight on shakes alone, but you’ll likely sacrifice muscle, upset your gut balance, and potentially undercut your long-term progress. On the other hand, a well-formulated whole-food diet can achieve the same calorie deficit while actively improving your health markers in the process.

It’s also a proud moment for Be Fit Food, the company whose meals were used for the whole-food VLED. The company was founded on the idea that “food is medicine,” and now they have solid scientific evidence backing that up.

The success of the whole-food group in this trial effectively establishes Be Fit Food as a scientific leader in real-food solutions for weight management and metabolic health. As the researchers noted, this is the first trial to directly pit food vs. meal replacements in a VLED context – and the food-based approach emerged clearly superior on multiple fronts.

For dietitians and clinicians, it sends a clear message: when prescribing rapid weight-loss programs, choose real food plans over packets of powder for better outcomes in body composition, gut health, and patient well-being.

Conclusion

The old saying “you are what you eat” gains new validity here. This study shows that how you lose weight matters just as much as how much weight you lose. Two people could eat 800 calories a day – one from balanced, whole-food meals and the other from processed shakes – and they’ll come out of the diet in very different health states.

The person eating real food is more likely to have lost mostly fat (not muscle), nurtured a healthier gut, and tuned up their metabolism for the better. The person solely on meal replacements will have lost weight too, but potentially at the cost of muscle, with a disrupted gut, and possibly more post-diet hunger or metabolic slowdown.

For the general public, the takeaway is empowering: you don’t need to rely on heavily processed “diet” products to achieve rapid weight loss. In fact, you might be much better off with a whole-food plan even if it’s low in calories. Whole foods provide a complexity that lab-made shakes simply can’t replicate – from tiny nutrients to fibre to natural plant compounds – all of which work together to keep your body functioning optimally during weight loss.

As the Food & Mood Centre researchers summarised, the healthiest path to weight loss is one that supports your gut and muscle, not just shrinks your waistline. So, if you or someone you know is considering a weight loss program, remember that real food is the real deal - and you don’t need to compromise on convenience to hit your daily targets. 

Your body will thank you – with better fat loss, a stronger microbiome, and a foundation for long-term health once the diet is over.

References

Lane M.M., McGuinness A.J., et al. (2025). Food- vs. supplement-based very-low-energy diets and gut microbiome composition in women with high body mass index: A randomized controlled trial, Cell Reports Medicine, 6(10), 102417.

Food & Mood Centre, Deakin University (2025). New study shows less processed diet may support healthier gut bacteria profiles during weight loss.