Calorie targets after bariatric surgery — why your app should never refuse the number

A beta tester emailed the team last week. She’d had bariatric surgery a few months earlier, was on a medically supervised post-op plan, and her calorie target was 880 per day. Two weeks of trying to set that number in Macroline’s iOS app — and the input field refused. “Enter a valid value,” the browser tooltip said.

She’s right and the app was wrong. We’ve shipped the fix. But the larger question is the one worth writing about, because it sits underneath nearly every nutrition app on the App Store: why does the input refuse a number a clinician already wrote down?

What’s actually clinical here

A few facts that get lost when “1200 minimum” gets baked into nutrition apps as a kind of cultural default:

Post-bariatric protocols run far below 1200 kcal in the early weeks, by design. The clinical practice guidelines cosponsored by AACE/ACE, The Obesity Society, ASMBS, the Obesity Medicine Association and ASA describe a staged progression — clear liquids, then full liquids, puréed, soft, then solids at four to six weeks — and put typical intake at about 400 kcal/day in the first week, progressing to 600–800 kcal/day by weeks three to four (Mechanick et al., Endocrine Practice, 2019, Recommendation R38). Intake climbs from there: the same guideline expects 1,200–1,500 kcal/day within several months and 1,500–1,800 long-term. So the very low numbers are real, they are prescribed, and they are temporary — monitored by the surgeon, the bariatric dietitian, and labs.

Very low calorie diets are defined as under 800 kcal/day, and they are clinical tools. Supervised VLCDs — commonly described in the 450–800 kcal range — are used before bariatric surgery to shrink liver volume, and in select non-surgical programs (Vilchez López et al., Nutr Hosp, 2013). A systematic review of nine studies found they reduced liver volume by 5–20% before surgery (Holderbaum et al., SOARD, 2018). They are not “extreme dieting.” They are a medical intervention.

GLP-1 receptor agonists routinely reduce intake below traditional “minimum” thresholds. In controlled trials, semaglutide cut how much people ate when given free access to food by 24% at 1.0 mg (Blundell et al., DOM, 2017) and 35% at 2.4 mg (Friedrichsen et al., DOM, 2021) versus placebo. Someone who used to maintain at 2200 may sit well below that for months without trying. This is the medication doing what it’s supposed to do.

The point isn’t that 880 calories is right for any specific person. It might be wildly wrong, depending on whose 880 we’re talking about. The point is that the number 880 is not, by itself, pathological. It can be exactly what a competent clinician prescribed, after careful consideration of body composition, surgery type, time since procedure, and labs.

When a tracking app refuses to accept it, the app is making a medical judgment it isn’t qualified to make.

Where the 1200-calorie floor comes from

It’s worth pausing on this, because it’s almost universal in consumer trackers.

Here is what the guidance actually says. The 2013 AHA/ACC/TOS obesity guideline and the Academy of Nutrition and Dietetics both list “1,200–1,500 kcal/d for women and 1,500–1,800 kcal/d for men” as one of three optional ways to create a deficit — the alternatives being a straight 500 or 750 kcal/day deficit, or an evidence-based dietary pattern. It appears as the bottom of a suggested prescription range, not as a floor below which intake is forbidden. ACSM’s position stand is deficit-based and names no floor at all. The nearest thing to a real caution comes from the 2025 joint GLP-1 advisory, which flags micronutrient adequacy as a concern below roughly 1200 kcal/day for women — a reason to watch nutrients and labs, not a prohibition. The current evidence-based view, where there is one, is that calorie targets are individualized — a function of body composition, metabolic context, medical history, and (when relevant) surgical or pharmacological intervention.

The 1200-floor lives on in trackers for two reasons. The first is genuine: some app builders are trying, awkwardly, to discourage disordered restriction. The second is liability theater: it’s easier to refuse low numbers than to think clearly about which low numbers are which.

But here’s what the refusal actually does:

A bariatric patient gets told by her surgeon to track at 800. The app refuses. She moves to a competitor that accepts the number — usually a less careful competitor — or she gives up tracking and loses the most useful tool she had for catching protein gaps.
A GLP-1 patient eating 1050 because she literally cannot eat more gets told by the app that her intake is dangerous. She blames herself. She over-rides and logs phantom food. The app’s data is now garbage.
A pre-bariatric VLCD patient on a 700-kcal liver-shrinking protocol can’t track at all for the four weeks before surgery — the period when adherence matters most.

The number isn’t the danger. Refusing to trust the user (and their clinician) is.

What “disordered restriction” actually looks like — and what to do about it

The harder, more honest question is: how does an app distinguish a clinically prescribed low target from someone in active disorder?

The honest answer is: it can’t. Not from a single number in a goal field. A 19-year-old logging 600 with no other context might be a pre-bariatric patient, an athlete in pre-competition water-cut (also clinical), or someone in a real eating disorder. The number alone won’t tell you.

What you can do — and what we’d push every tracker to do, including ours — is support the clinician relationship rather than substitute for it. That looks like:

Accept the number. Don’t quantize. Don’t impose a “common-sense” floor. Validate against obvious typos (zero, negative, an absurd >20,000) and otherwise trust the user.
Surface a contextual note for low targets the first time a user sets one. Not blocking, not paternalistic: a one-time “If a clinician didn’t prescribe this, we’d encourage you to talk to one before targeting it — here are resources.” Acknowledge that the user may already be working with one.
Don’t notify them they’re below a goal. A bariatric patient hitting 720 at 7 PM doesn’t need a push notification telling them they’re under. They know.
Provide eating-disorder resources discoverably. The NEDA helpline (1-800-931-2237, U.S.) and equivalent international lines should be findable without being moralized about.
Let them export. A user who decides this isn’t the right tool should be able to take their data with them — to a clinician’s office, to a different app, anywhere. Trapping data is its own quiet harm.

The framing worth holding onto, as a tool designer, is: the user is the expert on the user’s situation, in collaboration with their clinical team. An app’s job is to make tracking honest, not to make medical decisions through input validation.

What Macroline got wrong, and the fix

The actual bug in the iOS Goals editor was technically not a “minimum” — it was a step constraint. The HTML number input had step="50", which means the browser refuses any value that isn’t a multiple of 50. 880 is not a multiple of 50. The error message — “Enter a valid value” — is uninformative to a user who has no reason to know the input is quantized.

The macros had step="5", which broke values like 33 g protein. The calorie input also had a 500-kcal minimum baked into the backend validation. All three constraints were unnecessary, none were medical, and combined they made the app’s input layer functionally hostile to anyone with a non-round number.

We’ve shipped fixes across all three layers — the iOS app, the web app, and the backend. The new behavior: typo protection only. The minimum is 100, which exists to catch zero/single-digit input errors. The step is 1.

This was a small bug with a large message attached. If your tracker won’t let you set the number your surgeon wrote down, that’s a design statement about how it sees you. We’d rather not make that statement.

Macroline builds a food tracker. We’re not a medical provider, and this isn’t medical advice. Targets, including the low-calorie ranges discussed above, should be set in consultation with your bariatric team, GLP-1 prescriber, or registered dietitian. If you or someone you know is struggling with disordered eating, the National Eating Disorders Association helpline is 1-800-931-2237 (U.S.); international resources are at neda.nationaleatingdisorders.org/help-support/contact-helpline.