Therapeutic smoothies: what the word promises and what it delivers

In Switzerland, a manufacturer who printed “therapeutic smoothie” on a bottle would be breaking the law. Article 12 of the Foodstuffs and Utility Articles Ordinance prohibits statements that attribute to a food any property of preventing, treating or curing a human disease, and separately prohibits any presentation suggesting that a food is a therapeutic product. Only two exceptions exist: nutrition claims, and the health claims listed in Annex 14 of the Ordinance on Food Information.

That constraint is not bureaucratic trivia. It describes precisely what a blend of fruit and vegetables is allowed to claim: contributing to the normal functioning of a system, never repairing it or pushing it beyond normal. The officially authorised wording for vitamin C is that it “contributes to the normal function of the immune system”. The word normal is doing all the work in that sentence.

The rest of this article takes that framing seriously. You will find five recipes recalculated from the Swiss Food Composition Database, what the research actually shows about blending, satiety and sugar, and three cautions missing from almost all popular writing on smoothies.

What the word therapeutic usefully replaces

The intention behind “therapeutic smoothie” is reasonable: build a glass around a goal rather than at random. That is a good idea. The problem lies in the verb, not in the approach.

Three sentences can describe the same drink with wildly different degrees of truth. “This smoothie boosts your immunity” is false and, on a label in Switzerland, illegal. “This smoothie supplies 150 mg of vitamin C, or 187 per cent of the nutrient reference value, and vitamin C contributes to the normal function of the immune system” is true, checkable and compliant with Annex 14. “This smoothie gets me three portions of vegetables I would not otherwise have eaten” is probably the most useful of the three.

That last sentence deserves attention. Swiss dietary recommendations from the Swiss Society for Nutrition and the Federal Food Safety and Veterinary Office call for five portions a day, three of vegetables and two of fruit, with one portion equal to 120 grams. Most adults fall short. A smoothie that adds vegetables to a day that lacked them does something real. That does not turn it into medicine.

How many portions a smoothie actually counts for

This is the point nearly every smoothie recipe skips, and it is the one that most changes where a smoothie belongs in a day.

Swiss dietary recommendations are explicit: you may occasionally replace one portion of fruit or vegetables with 2 decilitres of 100 per cent juice with no added sugar, but no more than four portions per week, because juice no longer contains everything the whole food does and is not very filling. The NHS goes further: 150 ml of juice or smoothie counts as one portion at most, and that ceiling applies to the whole day regardless of how much you drink.

The smoothie sits in a middle position that neither authority resolves perfectly. Unlike juice, it keeps the fruit’s fibre, since the whole flesh goes into the jug. Unlike whole fruit, it destroys the cell structure. That distinction has measurable consequences, and they cut both ways.

The NHS classes sugars in smoothies as free sugars, alongside honey and syrup, precisely because blending or pressing releases them from the fruit matrix. The British ceiling for an adult is 30 g of free sugars a day. A 400 ml smoothie built on two bananas and a mango can reach 40 g on its own. The sugar is chemically identical to the sugar in the whole fruit, but its classification changes because the speed at which it is released changes.

A sensible position: count a fruit-led smoothie as one portion of fruit, not three, and drink it with a meal rather than between meals. For mostly vegetable smoothies with little fruit, the free-sugar argument carries far less weight.

What blending actually changes

Received wisdom says blending a fruit spikes blood glucose faster than eating it whole. A trial published in Nutrients in 2022 tested that directly and found the opposite.

Twenty healthy young adults, twelve women and eight men, ate the same fruit, deseeded gala apple and blackberries, once whole and once blended. Maximum glucose and incremental area under the curve were significantly lower after the blended version, and 60-minute glucose was marginally lower. The authors suggest an explanation: grinding the blackberry seeds releases fibre and nutritive components that would otherwise stay locked away.

The result covers one fruit combination and twenty participants. It does not mean every smoothie lowers blood glucose. It is enough, though, to retire the opposite claim, repeated without a source, that blending mechanically turns fruit into fast sugar.

The documented effect of blending lies elsewhere: in satiety. A crossover trial published in Nutrients in 2018 compared several preparations of identical energy value, 569 kJ, in healthy adults. Fullness varied with how food-like the preparation seemed and how quickly it was consumed. Energy intake compensation at the next meal did not differ between liquid preloads and the solid equivalent, but it collapsed over time: 82 per cent compensation when the meal followed two minutes later, only 12 per cent when it followed two hours later.

The practical conclusion is sharp. A smoothie drunk two hours before a meal will barely reduce what you eat at that meal. If you use it to replace a meal, it needs enough substance to hold: protein, fat, fibre, not blended fruit alone.

Blending and juicing are not the same thing

The two processes get lumped together in everyday talk, and the research separates them clearly.

A meta-analysis of prospective cohort studies published in 2025 in the American Journal of Medicine pooled fourteen cohorts on fruit juice and type 2 diabetes. For juice overall it found no significant association, with a relative risk of 1.06 and a confidence interval of 0.98 to 1.15. Broken down by type, juice containing less than 100 per cent fruit was significantly associated with increased risk, relative risk 1.15 with an interval of 1.03 to 1.28, while 100 per cent juice showed no significant association. The authors note that unlike whole fruit, 100 per cent juice showed no beneficial effect either.

A review in the Nutrition Bulletin, also from 2025, puts that in context. Processing and storing 100 per cent juice reduces its fibre, vitamins and antioxidants and converts the fruit’s intrinsic sugars into free sugars. Fruit eaten in solid form is more satiating because gastric emptying is delayed. And the interplay of polyphenols and fibre in whole fruit acts as a prebiotic in the gut. The authors therefore recommend that US dietary guidelines emphasise whole fruit more clearly and set an explicit ceiling for juice.

For smoothies the conclusion is mixed and not comfortable. A smoothie sits closer to whole fruit than juice does, because the fibre stays in the glass. On free sugars it sits closer to juice, because the cell structure is destroyed. If you want the fibre without the sugar spike, blend vegetables with a little fruit rather than the other way round.

Immunity: what is established and what is not

Vitamin C underpins nearly every smoothie recipe sold as an immunity drink. Its scientific record is long, thick and less dramatic than the marketing suggests.

The Cochrane review by Hemilä and Chalker, updated in 2013, pooled 29 comparisons and 11,306 participants taking at least 0.2 g of vitamin C daily on a regular basis. The relative risk of catching a cold in the general population was 0.97, with a 95 per cent confidence interval of 0.94 to 1.00. In other words, nothing clinically useful. In 598 marathon runners, skiers and soldiers on subarctic exercises, relative risk dropped to 0.48, which is substantial, but that subgroup does not resemble the person making a morning smoothie.

Two findings remain positive. Regular supplementation shortened colds by 8 per cent in adults and 14 per cent in children. On a seven-day cold, 8 per cent is about thirteen hours. And crucially, taken once symptoms appear, vitamin C showed no consistent effect across seven comparisons and 3,249 episodes. The smoothie you make on the morning you already feel rough will not shorten your cold.

What Annex 14 of the Ordinance on Food Information permits you to say matches that picture fairly well. Vitamin C, zinc, iron, copper, folate, selenium and vitamins A, B6, B12 and D all “contribute to the normal function of the immune system”, provided the food is at least a source of the nutrient under Annex 13. The nutrient reference value is 80 mg for vitamin C, 10 mg for zinc, 14 mg for iron. A solid food qualifies as a source from 15 per cent of that value per 100 g.

A well-built smoothie clears those thresholds easily for vitamin C. It is mediocre for zinc and iron, and useless for vitamin D, which remains the genuine weak point of Swiss winter intakes.

Digestion: three ingredients, three levels of evidence

Digestive recipes tend to pile up papaya, fennel, mint and ginger. Those four ingredients have nothing like the same evidence base.

Kiwifruit holds up best. A 2022 systematic review with meta-analysis in the Canadian Journal of Gastroenterology and Hepatology pooled seven randomised trials and 399 constipated participants, 82 per cent of them women, mean age 42. Against placebo, kiwifruit or its extracts increased weekly spontaneous bowel movements by 1.36, with a confidence interval running from -0.44 to 3.16, which crosses zero. Certainty of evidence was rated low. Against psyllium, kiwifruit did slightly better on frequency and on stool consistency, with moderate certainty for the first. The authors conclude the results are promising but that larger, more rigorous trials are needed.

Ginger has solid evidence, but for something other than everyday digestion. A meta-analysis of ten trials published in 2025 in the American Journal of Translational Research reports an odds ratio of 0.41, confidence interval 0.22 to 0.79, for reducing nausea and vomiting in hyperemesis gravidarum. Tolerance was good. Ginger against nausea therefore has a real basis; ginger against bloating after a heavy meal does not have the same file.

Mint works through a documented mechanism that turns against some people. A 2023 review in Current Pharmaceutical Design summarises that peppermint oil and its constituents relax the smooth muscle of the lower oesophageal sphincter, stomach, duodenum and large bowel. That relaxation explains its value in irritable bowel syndrome and functional dyspepsia. It also explains why it often worsens gastro-oesophageal reflux: the sphincter that relaxes is exactly the one that should stay shut. If you get acid reflux, mint is the wrong choice, and most digestive smoothie recipes never mention it.

Papaya and its enzymes are the weak link. Papain is an excellent meat tenderiser in vitro. Its effect on human digestion after swallowing, in a stomach whose pH drops below 2, is not established by convincing trials. Put papaya in a smoothie because it tastes good and carries carotenoids, not because its enzymes are doing measurable work in your gut.

Energy: the vaguest of the three words

“Energy” covers two things that have little in common: calories, measured in kilojoules, and the feeling of vitality, which cannot be measured directly.

On the first meaning, a smoothie does supply energy, sometimes more than people expect. The banana and cocoa recipe below provides 326 kcal, more than a slice of bread with jam. Presented as a light snack, it is not one.

On the second meaning, the authorised claims are precise and modest. Annex 14 allows the statement that vitamin C “contributes to the reduction of tiredness and fatigue”, with equivalent wording for iron, magnesium and several B vitamins. Those claims describe a metabolism functioning normally when intakes are covered. They do not describe a lift.

Chronic fatigue has causes a smoothie does not address: poor sleep, iron deficiency with or without anaemia, hypothyroidism, depression, sleep apnoea. If you have been tired for weeks, the matter belongs with a doctor and a blood test, not a recipe. That sentence is missing from nearly every article on energising smoothies, and it is the most important one in this section.

Five weighed recipes, calculated from Swiss data

The figures below come from the Swiss Food Composition Database, applied to the weights given. Percentages refer to the nutrient reference values in Annex 13: 80 mg vitamin C, 14 mg iron, 800 mg calcium, 375 mg magnesium, 2,000 mg potassium. The fibre benchmark is the WHO figure of at least 25 g a day for anyone over ten.

Orange, carrot and spinach

260 g orange, 60 g raw carrot, 30 g raw spinach, 1 cm grated fresh ginger, water to taste.

This glass supplies 150 kcal, 149 mg of vitamin C or 187 per cent of the reference value, 537 µg retinol equivalents, 9.2 g of fibre or 37 per cent of the daily benchmark, and 777 mg of potassium. It is the most micronutrient-dense of the five for the fewest calories. The ginger earns its place on flavour, and on an antiemetic effect where the context calls for one.

Kale, kiwi and banana

40 g raw kale, 150 g kiwifruit, 100 g banana, 150 ml oat drink fortified with calcium and vitamins, 10 g chia seeds.

315 kcal, 155 mg of vitamin C or 193 per cent of the reference value, 371 mg of calcium or 46 per cent, 13.4 g of fibre or 54 per cent of the benchmark, 1,040 mg of potassium. The calcium comes mainly from the fortified drink and from kale, which carries 240 mg per 100 g. The 0.4 µg of vitamin B12 comes solely from fortification of the plant drink: no unfortified plant ingredient provides any.

Pear, cucumber and flaxseed

200 g pear, 120 g cucumber, 10 g ground flaxseed, a few fresh mint leaves, water.

176 kcal, 9.4 g of fibre, 496 mg of potassium, and only 20 g of sugars. It is the least sugary of the set and the best fit for digestive comfort. Reminder from the previous section: avoid it if you have reflux, because of the mint.

Banana, oats and cocoa

120 g banana, 30 g rolled oats, 200 ml fortified almond drink, 10 g unsweetened cocoa powder.

326 kcal, 9.8 g of protein, 6.4 mg of iron or 46 per cent of the reference value, 142 mg of magnesium or 38 per cent, 9.9 g of fibre. The iron figure needs an important caveat: this is non-haem iron, absorbed far less efficiently than iron from animal sources and heavily dependent on the rest of the meal. Cocoa also brings polyphenols that inhibit that absorption. The iron on the label is not the iron you absorb.

Spinach, apple and oats

50 g raw spinach, 150 g apple, 100 g banana, 30 g rolled oats, water.

295 kcal, 55.6 g of carbohydrate, 8.9 g of fibre, 912 mg of potassium, 48 mg of vitamin C. It is the closest to a full breakfast, and the one that holds up best before physical activity. The raw spinach raises a question the next section addresses.

What Annex 14 lets you say about a smoothie

Anyone wanting to know where the line falls between a lawful statement and an advertising promise will find it written out in Annex 14. The list is closed: only the wordings listed there may be used, and only where the food is at least a source of the nutrient concerned under Annex 13.

For the nutrients a smoothie can realistically supply, the authorised sentences run as follows. Vitamin C contributes to the normal function of the immune system, contributes to the reduction of tiredness and fatigue, contributes to normal collagen formation for the normal function of blood vessels, bones, cartilage, gums, skin and teeth, contributes to normal energy-yielding metabolism, contributes to the normal function of the nervous system, contributes to normal psychological function, and increases iron absorption. Iron contributes to the normal function of the immune system, to normal energy-yielding metabolism and to the reduction of tiredness and fatigue. Magnesium likewise contributes to the reduction of tiredness and fatigue. Potassium contributes to the normal function of the nervous system.

Two observations follow. First, every one of those sentences contains the word normal or describes a contribution, never an increase beyond normal. Second, the last vitamin C claim, that it increases iron absorption, is the most practically interesting of the lot for a vegetarian. It describes exactly what a vitamin C rich smoothie can add to an iron-containing meal, and it appears in those words in the regulation.

What is missing from the list is just as telling. No authorised claim covers “detoxification”, none covers “cleansing”, none covers boosting defences beyond normal. Those words are absent not because the authority overlooked them, but because no assessment dossier could support them.

Oxalates: the risk recipes leave out

Raw spinach, kale and beetroot are high in oxalates. At ordinary amounts this matters to almost nobody. At “cleanse” amounts it does.

A case published in 2018 in the American Journal of Kidney Diseases describes a 65-year-old woman who developed acute oxalate nephropathy after a green smoothie cleanse made from oxalate-rich leafy greens. Her kidney function was normal beforehand. She progressed to end-stage renal disease. Two predisposing factors were present: a history of gastric bypass and recent prolonged antibiotic therapy.

A second case, reported in 2022 in Case Reports in Nephrology, involves a 68-year-old man with adequate baseline kidney function who followed a daily oxalate-rich fruit and vegetable juice regimen for six months, heavy on spinach, with a calculated intake of around 1,500 mg of oxalate a day, roughly ten times a typical diet. Kidney biopsy showed extensive tubular deposits. A year later he remained on dialysis.

These cases are rare and involve extreme quantities over months. They do not make spinach dangerous. They mark out a boundary: the prudent approach rotates leafy greens rather than using raw spinach every day, drinks enough fluid, and is extra careful with a history of kidney stones, chronic kidney disease, gastric bypass or recent antibiotics. Cooking also cuts soluble oxalate content appreciably.

Interactions and contraindications worth knowing

Four situations deserve genuine care, and none of them appears in mainstream recipes.

Grapefruit interacts with many medicines. The FDA explains the mechanism: grapefruit juice blocks the CYP3A4 enzyme in the small intestine, so more of the drug reaches the blood instead of being metabolised. With some statins such as simvastatin and atorvastatin, that raises the risk of liver and muscle damage. The opposite effect exists too: with fexofenadine, grapefruit juice blocks transporters and reduces how well the drug works, which is why the label says not to take it with fruit juices. The amount of enzyme varies between individuals, so the severity of the interaction does too. If you take long-term medication, that question belongs with your pharmacist, not an article.

Vitamin K in leafy greens matters to anyone on a vitamin K antagonist such as acenocoumarol or phenprocoumon. The problem is not eating greens but eating them erratically: a week of daily spinach smoothies followed by a week without destabilises the INR. The rule is consistency, set with the doctor managing the treatment.

Cross-reactive allergies are more common with smoothie fruit than people assume. A cross-sectional study published in 2023 in Foods followed 133 adults allergic to banana: 83.5 per cent also reacted to kiwifruit, 71.1 per cent to avocado, 58.8 per cent to persimmon. A quarter of the reported reactions were severe. If you have already reacted to one of those fruits, combining them in a glass is not trivial.

Spirulina, finally, is absent from the recipes in this article, and the ANSES opinion explains why. The agency notes that spirulina products can be contaminated with cyanotoxins, bacteria or trace metals, and that levels of lead, mercury and arsenic exceeding European limits have been reported in commercial samples. It advises against spirulina for people with phenylketonuria, because of its phenylalanine content, and for people with an allergic predisposition, because of reported cases. On B12, one point should be clear: spirulina contains cobalamin analogues that do not replace a supplement. Our article on vitamin B12 needs and reliable sources covers that in detail.

Building a glass without a recipe

The template below works for most goals and avoids the two usual traps: the over-sugared glass and the glass that does not last until the next meal.

Start with 150 to 250 g of vegetables or low-sugar fruit. Cucumber, spinach, kale, raw courgette, carrot, fennel: they give volume and micronutrients without loading sugar.

Then add 100 to 150 g of fruit, preferably one kind. This is the sweet part and the part to cap. Two bananas plus a mango is the 40 g free-sugar glass described earlier.

Add a source of protein or fat. Thirty grams of rolled oats, ten grams of ground flax or chia, a spoonful of nut butter, or silken tofu. That is what separates a glass that holds from a glass that leaves you hungry an hour later. Our complete guide to plant proteins goes further on this point.

Top up with liquid, water or an unsweetened plant drink, and finish with a flavour accent: fresh ginger, cinnamon, lemon zest, unsweetened cocoa, fresh herbs.

One texture note: flax and chia swell by absorbing several times their weight in water. A smoothie that looks right when blended turns into a spoonable cream ten minutes later. Allow extra liquid if you are not drinking it straight away.

Preparation, storage and hygiene

Three simple rules cover the essentials.

Wash leaves before blending, including those sold pre-washed unless the bag explicitly says otherwise. A smoothie is never cooked; whatever is on the leaf ends up in the glass.

Drink within twenty-four hours and keep it refrigerated in a sealed container. Vitamin C degrades in air and light, and oxidation is accelerated by blending, which multiplies the exposed surface. A crossover trial published in Nutrients in 2025 compared the bioavailability of 101.7 mg of vitamin C in three forms in twelve adults: powder, raw fruit and vegetables, or juice. All three raised plasma vitamin C, with the highest area under the curve for juice. Blending therefore does not destroy vitamin C at the moment you drink it; prolonged storage is the problem.

Clean the blender jug immediately. A sugary fruit residue at room temperature is a growth medium, and the seal around the blade is the spot people forget.

Six common mistakes

Treating the smoothie as an addition to a meal rather than part of it. A 326 kcal glass on top of a full breakfast is still 326 kcal.

Stacking sweet fruit. Three fruits in one glass is roughly an entire day’s free sugars under the NHS ceiling.

Believing a smoothie replaces three portions of vegetables. Swiss recommendations and the NHS both cap the substitution at one portion.

Adding powders without knowing what is in them. Spirulina, chlorella, assorted superfoods: traceable origin matters more than the promise on the label. Our article on reading a nutrition label sets out what to look for.

Using the same raw spinach every day for months. Rotating leafy greens is the simple answer to the oxalate problem.

Expecting a smoothie to fix settled fatigue. It replaces neither sleep nor a blood test.

Adapting to different profiles

A healthy person on no medication can use these recipes as written, rotating the greens week to week.

Someone on a vitamin K antagonist should aim for consistency: a stable amount of leafy greens, agreed with the doctor monitoring the INR, rather than alternating green weeks and green-free weeks.

Someone prone to kidney stones should limit raw spinach and beetroot, drink enough fluid, and favour cooked greens, whose soluble oxalate content is markedly lower.

Someone with reflux should skip mint, whose relaxing effect on the lower oesophageal sphincter is documented, and watch citrus too.

Someone with diabetes can take the 2022 blending result at face value but should reason about the total carbohydrate load of the glass rather than its preparation method, and drink it with a meal.

A vegetarian or vegan should not count on a smoothie for vitamin B12, except through a fortified plant drink, and should remember that the iron in these recipes is non-haem. Our article on plant-based iron absorption explains which levers actually work.

What these figures do not tell you

The recipe values come from generic entries in the Swiss database. Vitamin C in an orange varies with variety, ripeness and storage time; the gap between a fresh orange and one stored for weeks is real, and no table captures it.

The trials cited on blending and satiety involve twenty to fifty people, measured acutely. They describe an immediate physiological response, not a months-long effect on weight or blood glucose.

The oxalate nephropathy cases are individual reports, published precisely because they are rare. They establish that a risk exists at extreme doses; they support no estimate of frequency.

The health claims in Annex 14 rest on European assessment dossiers adopted into Swiss law. They describe normal physiological functions, not therapeutic effects, and their official wording is deliberately cautious.

Frequently asked questions

Can I make a smoothie the night before? Yes, refrigerated in a sealed container, drunk within twenty-four hours. Some vitamin C degrades and the texture shifts as the seeds swell, but most of the fibre, minerals and carotenoids survive.

Can a smoothie replace a meal? It can if it contains protein, fat and fibre rather than fruit alone. The 2018 compensation trial shows that a liquid preload taken two hours before a meal barely reduces what follows.

Should I peel fruit and vegetables? Not necessarily. Apple, cucumber and kiwi skins concentrate fibre and phenolic compounds. Wash them thoroughly. For citrus, remove the bitter white pith.

Do smoothies cause weight gain? No single food does that on its own. A 326 kcal smoothie drunk on top of normal meals adds calories; the same glass instead of breakfast changes nothing or reduces intake.

Does blending destroy vitamins? Not at the moment you drink it. The 2025 crossover trial shows good vitamin C bioavailability in juice form. It is prolonged exposure to air and light that degrades it.

Is spirulina worth it? For B12, no: its analogues do not replace a supplement. Otherwise, ANSES flags a risk of contamination with cyanotoxins, bacteria and heavy metals depending on the batch, and advises against it in phenylketonuria or allergic predisposition.

How many smoothies a day? One is enough, and it counts as one portion at most out of the recommended five. Swiss recommendations cap juice substitution at four portions a week.

Warm or cold? Cold, by habit. Nothing forbids a lukewarm smoothie, especially in winter, but avoid heating beyond body temperature if you care about vitamin C, which is heat sensitive.

Buying and storing in Switzerland

Two practical points concern Swiss retail and rarely appear in international recipes.

With plant drinks, fortification decides everything. An unfortified oat drink supplies almost no calcium, around 1 mg per 100 g, while the version fortified with calcium and vitamins sits near 110 mg per 100 g, plus B12 and vitamin D. The difference appears in small print in the ingredient list, not on the front of the carton. For anyone eating vegetarian or vegan, the fortified version is the more useful choice in a smoothie.

Frozen berries and leafy greens make a sensible base. Swiss dietary recommendations note that frozen fruit and vegetables are processed soon after harvest and largely retain their vitamins and minerals, while tinned produce is less nutritious but keeps well in a cupboard. For smoothies, frozen berries have the added advantage of chilling the mix without diluting it the way ice cubes do.

Going further

On related topics, see our article on green smoothies and immunity, the one on balanced smoothies combining fruit, vegetables and protein, and the local combinations without exotic fruit. On sugar, our decoding of natural alternatives and glycaemic index complements the free-sugar section. On ginger and turmeric, the piece on anti-inflammatory spices sets out the state of the evidence. And if your real goal is to drink better, our guide to hydration over 24 hours will serve you better than any smoothie recipe.

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