The Truth About Rapid Weight Loss No One Is Talking About

A randomised controlled trial led by Deakin University's Food & Mood Centre compared two very low energy diets in women with obesity over three weeks: one built from real food, one from shakes, soups and bars. Both were matched at roughly 800–900 calories a day and matched for macronutrients [1].

We are going to give you the headline result first, because it is the one most likely to be spun.

On weight loss, the two were the same

Modified intention-to-treat: the food group lost 4.58 kg, the supplement group lost 4.85 kg. No significant difference between them.

So we are not going to tell you our food takes off more weight than a shake. At matched calories it does not, and a trial we part-participated in says so. Anyone claiming otherwise is selling you something.

What the trial was actually designed to measure was different — the primary endpoint was species-level alpha diversity of the gut microbiome, not kilograms. That is where the two approaches came apart.

Where they differed

There was also a body-composition signal: the whole-food group showed less reduction in hip circumference, which the trial authors discussed as potentially consistent with better preservation of lower-body lean tissue. We want to be careful here — that is an indirect signal, not a direct measurement of body composition. It is a reason to be interested, not a finding to lean on.

Why the microbiome matters for appetite

This is the part that connects a gut finding to whether you can actually stay on a diet.

Microbial fermentation of dietary fibre produces short-chain fatty acids, and those are involved in signalling pathways linked to the satiety hormones GLP-1 and PYY. Feed the bacteria that make them, and you are working with your appetite rather than against it. Remove the fibre, and you are not.

What your body does when you lose weight

Two adaptations work against you, and neither is a matter of willpower.

Leptin signals energy sufficiency and satiety, and it usually falls as you lose weight. Ghrelin may rise, increasing the biological drive to eat. Reviews show these adaptations may favour regain — though hormone changes alone do not perfectly predict who regains, and we should not overstate how deterministic this is.

The practical reading: if you found maintenance harder than the losing, that is a described physiological pattern, not a personal failure.

The muscle problem

Losing a large proportion of lean tissue reduces resting metabolic rate, worsens functional capacity, and makes maintenance harder. It is the quiet cost of rapid weight loss done carelessly.

Reviews emphasise two mitigations: adequate protein, and where possible resistance training. Neither is optional if you are running a very low energy diet and want to keep the result.

Our meals are built with that in mind — around 20–30 g of protein per meal, low carbohydrate, natural fibre and phytonutrients, and between 4 and 12 vegetables per meal.

What a shake cannot do

Beyond the trial data, there is a structural argument worth making plainly. A meal replacement cannot teach you meal structure, protein distribution, portion awareness, food variety, or any sustainable eating behaviour — because there is no meal to learn from.

That matters most at the end. A shake-based program gives you nothing to transition onto, which is precisely the moment most weight comes back. Real food is harder to formulate and easier to keep doing.

What we claim, and what we do not

We claim the trial found comparable weight loss and better gut microbiome outcomes on a whole-food very low energy diet. That is what it found.

We do not claim our meals produce more weight loss than shakes, that the microbiome differences have been shown to translate into long-term clinical outcomes, or that the hip circumference signal proves lean mass was preserved. Three weeks is a short trial in a specific population, and it should be read as such.

Before you start

A very low energy diet is not suitable for everyone. If you take prescribed medication, manage a health condition, or are pregnant or breastfeeding, speak to your GP or one of our Accredited Practising Dietitians first. The consultation is free, 15 minutes, by video or phone, valued at $49.

Reference

  1. Lane MM, McGuinness AJ, Mohebbi M, Lotfaliany M, Loughman A, O'Hely M, O'Neil A, Batti J, Kotowicz M, Berk M, Saunders L, Page R, Beattie S, Marx W, Jacka FN, et al. 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 2025;6(10):102417. doi:10.1016/j.xcrm.2025.102417

Important health information

This article carries no health disclaimer of its own while discussing very low energy dieting, hormonal adaptation and metabolic outcomes. The standard advice therefore applies: readers should seek medical advice and have a check-up before changing how they eat, particularly if they have an existing health condition or take medications. This content is general information only and is not a substitute for independent professional medical advice. A very low calorie or very low energy diet is a significant intervention, was studied here over three weeks in women with obesity under trial conditions, and is not appropriate for everyone - it should be undertaken with medical or dietetic supervision.

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Questions and answers

What do we explain about The Truth About Rapid Weight Loss No One Is Talking About?

On our The Truth About Rapid Weight Loss No One Is Talking About page, we explain that a randomised controlled trial led by Deakin University's Food & Mood Centre compared two very low energy diets in women with obesity over three weeks: one built from real food, one from shakes, soups and bars. Both were matched at roughly 800–900 calories a day and matched for macronutrients [1]. We are going to give you the headline result first, because it is the one most likely to be spun.

What should I know about on weight loss, the two were the same on this page?

On our The Truth About Rapid Weight Loss No One Is Talking About page, we explain that modified intention-to-treat: the food group lost 4.58 kg , the supplement group lost 4.85 kg . No significant difference between them. So we are not going to tell you our food takes off more weight than a shake. At matched calories it does not, and a trial we part-participated in says so. Anyone claiming otherwise is selling you something. What the trial was actually designed to measure was different — the primary endpoint was species-level alpha diversity of the gut microbiome , not kilograms. That is where the two approaches came apart.

What should I know about where they differed on this page?

On our The Truth About Rapid Weight Loss No One Is Talking About page, we explain that microbiome diversity improved significantly more on the whole-food diet. Species richness improved more. The whole-food approach better preserved fibre-degrading, health-associated taxa — the bacteria that do the useful work. There was also a body-composition signal: the whole-food group showed less reduction in hip circumference, which the trial authors discussed as potentially consistent with better preservation of lower-body lean tissue. We want to be careful here — that is an indirect signal, not a direct measurement of body composition. It is a reason to be interested, not a finding to lean on.

What should I know about why the microbiome matters for appetite on this page?

On our The Truth About Rapid Weight Loss No One Is Talking About page, we explain that this is the part that connects a gut finding to whether you can actually stay on a diet. Microbial fermentation of dietary fibre produces short-chain fatty acids, and those are involved in signalling pathways linked to the satiety hormones GLP-1 and PYY. Feed the bacteria that make them, and you are working with your appetite rather than against it. Remove the fibre, and you are not.

What should I know about what your body does when you lose weight on this page?

On our The Truth About Rapid Weight Loss No One Is Talking About page, we explain that two adaptations work against you, and neither is a matter of willpower. Leptin signals energy sufficiency and satiety, and it usually falls as you lose weight. Ghrelin may rise, increasing the biological drive to eat. Reviews show these adaptations may favour regain — though hormone changes alone do not perfectly predict who regains, and we should not overstate how deterministic this is. The practical reading: if you found maintenance harder than the losing, that is a described physiological pattern, not a personal failure.

What should I know about the muscle problem on this page?

On our The Truth About Rapid Weight Loss No One Is Talking About page, we explain that losing a large proportion of lean tissue reduces resting metabolic rate, worsens functional capacity, and makes maintenance harder. It is the quiet cost of rapid weight loss done carelessly. Reviews emphasise two mitigations: adequate protein , and where possible resistance training . Neither is optional if you are running a very low energy diet and want to keep the result. Our meals are built with that in mind — around 20–30 g of protein per meal, low carbohydrate, natural fibre and phytonutrients, and between 4 and 12 vegetables per meal.

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