How the score works

What the score tells you

Each meal gets a score from 1 to 10. It says how close that plate came to a balanced one for your goal and your body. You take a photo; you don’t weigh, measure or count anything.

From photo to plate

An AI model reads the photo and estimates two things. First, how the food splits into veggies (non-starchy vegetables and fruit; potatoes and corn count as carbs), protein, carbs and fats. Second, how big the portion is, measured against the hand in your shot, or against the plate and cutlery when there is no hand. It also notes ultra-processed food, visible added sugar and alcohol. A short note, spoken or typed, helps with what a camera can’t see.

The AI doesn’t pick the score. It reports what it reads from the photo, including a rough guess at hidden oil, and a fixed formula on Portion’s server turns that reading into the number.

The target plate for your goal

The base is the Harvard Healthy Eating Plate: half vegetables and fruit, a quarter protein, a quarter whole grains. Portion gives fats a tenth of every plate, since cooking oil and dressings are rarely visible. Of the other nine tenths, each goal sets the split:

• Lose weight: 50% veggies, 25% protein, 25% carbs
• Eat balanced: 37.5% veggies, 25% protein, 37.5% carbs
• Gain weight: 25% veggies, 25% protein, 50% carbs
• Build muscle: 25% veggies, 30% protein, 45% carbs

Build muscle is the one goal where the protein share grows: people training to build muscle are advised to eat more of it (Jäger et al., 2017; Iraki et al., 2019).

How big the plate should be

Portion estimates how much energy a body needs from sex, age, height and weight, using the equations in the US National Academies’ 2023 report on energy needs (NASEM, 2023). It compares that with a reference adult (35 years old, 170 cm, 70 kg) and scales the plate to match: more need, bigger plate. Three more things adjust it:

• Activity: you pick a level, or, if you switch on Activity from steps, the app sets it from your average step count.
• Goal: Lose weight makes the plate a little smaller. The other goals change what’s on the plate, not how much.
• Meals per day: the day’s amount is split across your meals, so five meals mean smaller plates than three.

With Activity from steps, under 5,000 steps a day counts as sedentary (Tudor-Locke et al., 2013). The other bands follow Tudor-Locke & Bassett, 2004: 5,000–7,499 light, 7,500–9,999 moderate, 10,000–12,499 active, 12,500 or more very active. Steps miss strength training, cycling and swimming, and walking alone takes far more than 10,000 steps a day to reach the energy use the equations call active (Ohkawara et al., 2011), so if you train, pick your level by hand.

A floor keeps the plate from shrinking too far. It is based on the lower end of the daily calorie ranges that the 2013 obesity guideline of the US heart and obesity societies gives for weight-loss diets. An upper limit keeps unusual profiles from producing an oversized plate.

The hand as a ruler

A photo shows what’s on the plate, not how big it is. A hand resting beside the food is a ruler you always carry. Medicine works the same way: clinicians size a burn or a rash against the patient’s own hand, which covers just under 1% of an adult’s skin on average (Rhodes et al., 2013).

Hands differ, so when your profile has your height, Portion adjusts the ruler to the typical hand for your height and sex. The link comes from ANSUR II, a measurement survey of about 6,000 adults: height and sex together explain around 70% of the variation in hand size, taller people have bigger hands, and men’s are larger than women’s at the same height. That is enough to adjust the ruler, not to replace the photo, and it assumes the hand in the shot is yours.

For the score, the hand is only a ruler: it sets the scale, and the target portion comes from your body, not from a fist-and-palm chart.

How the score comes together

The score asks two questions at once: are the proportions right, and is the plate the right size for you? Each part (veggies, protein, carbs, fats) is compared with its target amount, which already reflects your goal and your body.

Falling short lowers the score, except for fat: too little fat is never penalized. Overshooting lowers it too, except for veggies: more veggies never hurt.

The four results are then combined in a way that punishes imbalance. One part far off drags the whole score down, which is why a plate of only rice can’t score well just because the carbs are right. Size works the same way: a perfectly proportioned plate at half or double the right size scores below one that fits. Ultra-processed food, visible added sugar and alcohol take points off, and alcohol takes more with every drink. How much depends on your goal.

Research supplies the inputs: the plate, the energy equations, hand size. How they combine into one number is Portion’s own design.

Past meals keep their score

A logged meal keeps the target it was scored with. Change your goal, weight or activity later and it applies from your next meal. Favorites are the exception: they always score against your current profile.

What the score can’t do

• Photos are estimates. Mixed dishes, layers and drinks are hard to read. With no hand in the shot and no sizes in your note, or a plate the AI couldn’t fully make out, the result is flagged as a rough estimate; so is a meal logged from a description alone. A photo that can’t be read gets a request for another shot or a short description, not a guessed number.
• Bodies vary. The equations describe a typical body and carry their own margin of error. Pregnancy, breastfeeding, medical conditions and medication aren’t modeled; if any of that applies, ask your doctor or dietitian how big your plate should be. For anyone under 19, the adult equations are only an approximation, and for anyone under 18 a weight-loss goal never shrinks the plate. Very heavy training may also lie beyond them: extra activity tends to raise the body’s total energy use by less than you’d expect (Careau et al., 2021).
• Snacks get a simple verdict, not a number. They still count toward your day.

This is general information, not medical advice. Your doctor or registered dietitian can tailor a plan to you. Follow their guidance. A score rates a plate, not you.

All sources

Every source named here, with its link, is on the sources page.