How to Read a Food Label for Weight Loss: What to Look for and What to Ignore

Food labels contain the information you need to make accurate calorie decisions — but they're structured in ways that routinely mislead people who don't know what to look for. The most important numbers are often buried, the most prominent numbers are often misleading, and manufacturer conventions around serving sizes are systematically optimistic. Here's how to read a label accurately for weight management purposes.

Start Here: Calories Per Serving vs Calories Per 100g

Every food label in the UK shows nutritional information in two columns: per 100g and per serving. These numbers serve different purposes and both matter — but for different reasons.

Per 100g is the comparison number. It tells you how calorie-dense a food is relative to its weight, regardless of how much you eat. Use the per-100g column when comparing two products to decide which is lower-calorie. A yogurt at 85 cal/100g is lower-calorie than one at 130 cal/100g, regardless of the pot sizes.

Per serving tells you what you actually get when you eat the stated portion. This is the number to log when tracking — but only if the stated serving size matches what you actually eat. If it doesn't, you need to calculate.

The Serving Size Trap

This is where most label-reading errors occur. Manufacturer serving sizes are set to show the food in the most favourable light, and they are frequently much smaller than the portions people actually eat.

Common examples:

Food	Stated serving size	Typical actual portion	Calorie difference
Breakfast cereal	30g	60-80g (bowl)	2-2.5x stated calories
Peanut butter	15g (1 tbsp)	25-35g (generous spread)	1.7-2.3x stated calories
Olive oil	10ml	15-25ml (pouring)	1.5-2.5x stated calories
Crisps / chips	25g	40-50g (standard bag)	1.6-2x stated calories
Granola	45g	80-100g (bowl)	1.8-2.2x stated calories
Pasta (dry)	75g	100-130g (typical portion)	1.3-1.7x stated calories

The practical rule: always check what the stated serving size is in grams, then compare it to what you actually eat. If the label says 150 calories per 30g serving and you eat 60g, you're consuming 300 calories — not 150. The label isn't lying; the serving size is just smaller than your portion.

The most reliable solution is to weigh your portion and calculate from the per-100g figure: (grams eaten ÷ 100) × calories per 100g = actual calories. For a 60g portion of cereal at 375 cal/100g: (60 ÷ 100) × 375 = 225 calories.

The Traffic Light System (UK)

Most UK packaged foods display a front-of-pack traffic light system showing green, amber, or red for fat, saturated fat, sugars, and salt — based on per-serving amounts. Understanding what it means (and what it doesn't):

• Green = low in that nutrient per serving. Does not mean the food is low-calorie overall.
• Amber = medium amount of that nutrient. Most foods land here for most nutrients.
• Red = high in that nutrient per serving. Does not mean don't eat it — it means be aware of how it fits into the day's total.

The traffic light system does not show calories — it shows fat, saturated fat, sugars, and salt. A food can be all-green on the traffic light and still be high in calories (e.g., a small portion of nuts: low sugar, low salt, but 600+ cal/100g). For weight management, the traffic light is a useful secondary tool but not a substitute for reading the calorie figure directly.

Protein and Fibre: The Two Numbers Worth Tracking

For weight loss purposes, beyond calories, the two most useful nutritional figures on a label are protein and dietary fibre. Both directly affect satiety — how long a food keeps you full — which affects how easy the calorie deficit is to maintain.

Protein is the most satiating macronutrient per calorie. A food that delivers 20g protein per 300-calorie serving will keep you fuller longer than one that delivers 5g protein at the same calorie count. For meals and snacks, aim for options that deliver the highest protein per calorie — the per-100g column makes this comparison easy.

Fibre slows gastric emptying and extends the satiety window. High-fibre foods (5g+ per 100g is the UK "high fibre" threshold) produce slower glucose release and longer satiety. A breakfast cereal with 8g fibre per 30g will sustain appetite suppression significantly longer than one with 1g fibre at the same calorie count.

A simple label-reading heuristic: for any food, calculate the protein-to-calorie ratio (grams of protein ÷ calories per 100g). Anything above 0.15 (15g protein per 100 calories) is a high-protein food. Cottage cheese: 11g protein / 72 cal per 100g = 0.15 — right at the threshold. Chicken breast: 31g / 165 cal = 0.19 — well above it. White bread: 7g / 265 cal = 0.03 — very low.

The Ingredients List

Ingredients are listed in descending order by weight — the first ingredient is present in the largest quantity, the last in the smallest. The first three ingredients tell you what the food primarily is.

Key things to read from the ingredients list:

• Sugar in the first three ingredients = the food is primarily sugar, regardless of what the front label says. "Muesli" with sugar listed second is a confectionery product dressed as a breakfast food.
• Multiple sugar aliases = the food contains more sugar than any single ingredient entry suggests. Glucose syrup, dextrose, maltose, fructose, concentrated fruit juice — all are sugars. When they appear as separate ingredients, each counts separately but they combine to a larger total sugar contribution.
• Whole grain vs refined grain = "wholegrain wheat" vs "wheat flour" (which is refined by default). Wholegrain is higher in fibre and produces a lower glycaemic response.
• Hydrogenated or partially hydrogenated oils = trans fats, which increase cardiovascular disease risk. Increasingly rare in UK food products but still present in some imported or budget products.

Carbohydrates: Total vs Sugars vs Fibre

The carbohydrate section of a UK label shows two figures: total carbohydrate and "of which sugars." This distinction matters for different purposes:

Total carbohydrate is what to use for calorie tracking — it includes all carbohydrates: starches, sugars, and fibre. All contribute the same 4 calories per gram in the standard calculation used on food labels.

Of which sugars shows the fast-digesting carbohydrate fraction — relevant for blood sugar management (particularly for people with insulin resistance, diabetes, or PCOS) and for identifying foods that are misleadingly labelled as healthy while being sugar-dense.

Fibre is listed separately under carbohydrates on UK labels. While technically a carbohydrate, dietary fibre contributes minimal calories (approximately 2 cal/g vs 4 cal/g for other carbohydrates) and slows the digestion of the other carbohydrates in the food. Some calorie tracking apps subtract fibre from total carbohydrates to show "net carbs" — the figure used in low-carbohydrate dietary approaches. For standard calorie counting, use total carbohydrate.

Calorie Density as a Label-Reading Tool

The calories per 100g figure doubles as a calorie density indicator — how many calories you get per gram of food. This is a practical satiety tool:

Calorie density	Range	Examples
Very low	<60 cal/100g	Most vegetables, broth, fruit
Low	60-150 cal/100g	Lean protein, low-fat dairy, legumes
Medium	150-300 cal/100g	Bread, cooked pasta, rice, eggs
High	300-500 cal/100g	Cheese, fatty meats, pastry
Very high	>500 cal/100g	Oils, butter, chocolate, nuts, crisps

Foods below 150 cal/100g can generally be eaten in larger portions without significant calorie cost. Foods above 300 cal/100g need careful portioning. The per-100g figure makes this immediately readable from any label without additional calculation.

"Low Fat," "Light," and Other Front-Label Claims

Front-of-pack claims are marketing, not nutritional guidance. UK regulations define what these terms can mean, but they are consistently misleading in practice:

• "Low fat" — defined as less than 3g fat per 100g. Low-fat versions of dairy foods (yogurt, cheese) are genuinely lower-calorie. But "low fat" crisps, biscuits, and snack foods often replace fat with sugar, producing similar or higher calorie counts with worse satiety. Always check the actual calorie figure.
• "Light" or "Lite" — must contain at least 30% less of a specific nutrient or calories than the standard version. "Light" olive oil is lighter in flavour, not in calories — it has virtually the same calorie count as regular olive oil. The comparison must be stated on the label; find it.
• "No added sugar" — means no sugar was added in processing. Does not mean the food is low in sugar. Fruit juices and dried fruit can be "no added sugar" while being very high in naturally occurring sugars.
• "Natural" — has no regulated meaning in the UK. Disregard it for nutritional purposes.
• "High protein" — defined as at least 20% of the food's calories coming from protein. Useful if you're prioritising protein, but always verify with the actual protein-per-100g figure rather than trusting the front label.

A Practical Label-Reading Sequence

When picking up a packaged food for the first time, in order:

1. Check calories per 100g — establishes calorie density and allows comparison with alternatives
2. Check the stated serving size in grams — compare to your actual portion; recalculate if different
3. Check protein per 100g — calculate protein-to-calorie ratio if satiety is a priority
4. Check fibre per 100g — 5g+ is high fibre; 3g+ is a source of fibre
5. Check the first three ingredients — tells you what the food actually is regardless of front-label claims
6. Ignore front-label marketing claims — verify anything interesting in the actual nutritional table

For ongoing tracking, see our guide on calorie tracking accuracy and our portion sizes guide — label reading and portion accuracy work together for reliable calorie tracking.

Summary

• Always check whether the per-serving figure matches your actual portion — serving sizes are systematically smaller than typical portions; multiply accordingly or calculate from per-100g
• Per-100g is for comparing products; per-serving is for logging what you eat — use both
• Protein and fibre are the two most useful figures beyond calories — they predict satiety per calorie more reliably than fat or sugar content
• Ingredients are listed by weight descending — the first three ingredients define what the food primarily is
• Front-label claims ("low fat," "light," "no added sugar") are marketing with specific regulatory definitions that are routinely misleading — verify with the nutritional table
• Calories per 100g is a direct measure of calorie density — foods below 150 cal/100g can be eaten in larger portions; foods above 300 cal/100g need careful portioning

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Related Reading

• Best Food Scale for Weight Loss: What to Look for and What Actually Matters
• Portion Sizes Explained — A Visual Guide to How Much You're Actually Eating
• How to Track Calories Without Weighing Everything
• Calorie Deficit for Beginners — How to Calculate Yours and Actually Maintain It
• Why Am I Not Losing Weight on a Calorie Deficit? A Troubleshooting Guide

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