High energy foods: what 'energy' really means, and the UK foods that carry the most

Written by James Frost, founder of Flaming Phoenix. Updated October 2026.

High energy foods are foods with a lot of calories: on UK food labels, “energy” means calories, in kilojoules (kJ) and kilocalories (kcal). Oils carry the most, about 900 kcal per 100g; in a normal portion, oily fish, pasta and roast chicken lead. Lists of foods that “give you energy” mean feeling alert, which labels do not measure.

Below: 25 everyday UK foods ranked by calories per portion, kJ and kcal explained, food for long active days and ideas for small appetites. For the per-gram ranking, where oils, butter and nuts lead, see my guide to the most calorie-dense foods.

What does “energy” mean on a food label?

On a UK food label, energy is the calorie content of the food, and the label has to give it in both kilojoules and kilocalories.

The NHS guide to reading food labels says the nutrition panel must show energy in kJ and kcal, and its page on calories tells you to look under the “energy” heading. Energy is the first line of the nutrition table, per 100g or 100ml and sometimes per portion, and the percentages on the front of packs use a reference intake of 8,400 kJ or 2,000 kcal for an adult.

To turn kilojoules into calories, divide by about 4.2: the NHS Eatwell Guide gives an average woman's 2,000 calories a day as 8,400 kJ and a man's 2,500 as 10,500 kJ. The result is close, not exact: porridge oats are 1,614 kJ and 381 kcal per 100g in the UK food tables, and 1,614 ÷ 4.2 is 384. The gap is there because each nutrient has its own kJ and kcal factor.

Where do the calories in food come from?

Calories on a label come from fat, carbohydrate, protein, fibre, alcohol and a few minor ingredients such as polyols, using the fixed factors in Annex XIV of the regulation. This table shows the main factors and what 10g of each supplies.

Fat gives more than twice as much as carbohydrate or protein, which is why the NHS notes that starchy foods have fewer than half the calories of fat, gram for gram. Water gives nothing. Raw spinach is about nine-tenths water, so an 80g portion is 20 kcal; one tablespoon of olive oil (11g in the British Dietetic Association's portion guide) is 99.

Is “high energy” a legal term?

No. Great Britain's rules on nutrition claims define “low energy”, “energy-reduced” and “energy-free”, but there is no “high energy” claim, so the phrase on a pack has no fixed meaning.

The GB nutrition and health claims register sets the limits: low energy means no more than 40 kcal (170 kJ) per 100g for a solid food or 20 kcal (80 kJ) per 100ml for a drink; energy-reduced means at least 30% less than usual; energy-free means no more than 4 kcal (17 kJ) per 100ml. To compare two foods, use the kcal per 100g on the back of each pack.

Why do “energy food” lists pick oats, bananas and spinach?

Most “energy food” lists use energy to mean feeling lively, and pick foods for their vitamins, fibre or carbohydrate instead of their calories.

The law is strict about that second meaning. The GB register allows the claim that a nutrient contributes to the reduction of tiredness and fatigue for nine vitamins and minerals only: folate, iron, magnesium, niacin, pantothenic acid, riboflavin, vitamin B6, vitamin B12 and vitamin C, and only on a food that is at least a source of that nutrient. It lists the claim that glucose contributes to normal energy-yielding metabolism as non-authorised, and in February 2019 the Advertising Standards Authority upheld a complaint about a glucose tablet poster on the London Underground for implying an immediate increase in energy levels.

Some list favourites hardly register in the label sense. The UK food tables give raw spinach 25 kcal per 100g, oranges 36 and blueberries 40, so all three sit within the legal limit for “low energy”. Eat them for other reasons; they add few calories.

So this page sticks to what foods contain. If you feel tired most of the time, the NHS advises seeing a GP when rest and sleep do not help.

Which everyday foods have the most energy per portion?

In a normal UK portion, grilled mackerel (396 kcal), baked salmon (325), boiled pasta (254) and roast chicken leg (212) carry the most calories of the everyday foods below; olive oil and butter fall near the bottom because their portions are small.

How the table works: kcal and kJ per 100g come from the UK's McCance and Widdowson food tables (CoFID 2021), multiplied by the adult portion sizes in the British Dietetic Association's portion guide and rounded. Sweet potato uses the BDA's baked potato portion; avocado, berries and spinach its 80g fruit and vegetable portion; milk is counted as 100g per 100ml. Brands differ, so check the pack you buy.

The per-portion order is close to the reverse of a per-gram list: olive oil has the most calories per 100g here (899), yet one tablespoon gives 99, while boiled pasta, at 169 per 100g, gives 254 because you eat 150g of it. And the banana (65), orange (29), blueberries (32) and spinach (20), all regulars on the “energy food” lists Google shows, give the fewest calories of anything in the table.

If you need more calories, look at what goes on top: a banana with 30g of peanut butter is 247 kcal (65 + 182), the banana alone 65.

How do you turn these foods into bigger meals?

Start with a starchy base or an oily fish, then add a fat or a dairy food: each plate below comes to between about 450 and 530 kcal using only BDA portions and the values in the table.

• Baked potato, beans and cheese: 180g potato (175) + 150g baked beans (122) + 30g Cheddar (125) + one teaspoon of butter (37) = 459 kcal.
• Pasta with olive oil and Cheddar: 150g cooked pasta (254) + one tablespoon of olive oil (99) + 30g Cheddar (125) = 478 kcal. Leave off the oil and cheese and it is 254.
• Salmon and rice: 140g baked salmon (325) + 150g boiled rice (197) = 522 kcal.
• Porridge with peanut butter: 40g oats (152) + 200ml whole milk (126) + 30g peanut butter (182) + one 80g banana (65) = 525 kcal.

Most of the extra calories come from the fat on top. The Eatwell Guide says all fats are high in energy (calories) and should be eaten in small amounts, which suits most people; if you need more calories, a spoon of oil or a slice of cheese is the simplest addition. My guide to eating more calories without eating more food goes meal by meal, high calorie porridge builds up the breakfast bowl, and there are separate lists of foods high in both calories and protein and high calorie snacks.

What should you eat for a long, active day?

For a long walk, ride or run, eat a starchy, lower-fat meal two to three hours before, carry carbohydrate to eat every hour if you will be out for more than an hour, and eat again soon after you finish. My high energy snacks guide turns that into snack tables with UK prices.

What is the difference between starch and sugars?

Both are carbohydrate at 4 kcal per gram, but the BDA describes free sugars as quickly broken down and absorbed, and starchy carbohydrates as taking longer to break down into glucose. This table splits common carbohydrate foods into the two, using CoFID values for the portion shown.

Sugar found naturally in whole fruit, vegetables and milk does not count as free sugars, the NHS explains, so the 14g in a banana is counted differently from the sugar in honey or jam. Sweet potato is the odd one out among the starchy foods: just over half its carbohydrate is sugars (26 of 50g). For comparison, a Vanilla Phoenix Bar has 66g of carbohydrate, of which 29g are sugars.

When should you eat before, during and after?

Before: the BDA's sport and exercise fact sheet suggests a low-fat, high-carbohydrate snack or light meal two to three hours before exercise. Jack Chamberlain, a customer, uses Phoenix Bars “as part of my quick and easy breakfast or pre-race meal 2 hours before races.”

During: sports scientist Asker Jeukendrup suggests no carbohydrate is needed for exercise under 30 minutes, about 30g an hour for one to two hours, and up to 60g an hour beyond that, rising to 90g past two and a half hours if your stomach copes.

After: the BDA advises starting to refuel as soon as possible with a high-carbohydrate snack or meal; a 150g portion of boiled pasta gives 56g. My page on hitting the wall covers what happens when carbohydrate runs short on a long effort.

Where does a dense bar fit on a long day?

If you are carrying your food, weight counts. A Phoenix Bar gives up to 557 calories in only 120g, with up to 66g of carbohydrate and up to 19g of protein, in six flavours. Half a Vanilla bar is 60g for 276 kcal and 33g of carbohydrate; two 80g bananas from the table give 130 kcal and 32g for 160g of fruit, before the skins. David Wilson, a customer, plans to use them “for any of my long days out in the outdoors to maximise my calorie intake.” On a short walk or a normal working day, ordinary meals cover it and a bar is more than you need. The range of high calorie bars I make is on the homepage, and my guide to the best food for hiking covers trail food more widely.

High energy foods for older people and small appetites

With a small appetite, the aim is more from each mouthful, not bigger plates. NHS dietitians use “high energy” in the label sense: Cambridge University Hospitals' leaflet on a high energy and protein diet is about calories and protein, and suggests:

• small amounts often, with snacks between meals and at bedtime;
• full-fat foods instead of light or diet versions;
• stirring milk powder into food: 4 tablespoons into a pint of full-cream milk, or 2 tablespoons into porridge, custard or a white sauce;
• not filling up on bulky foods such as a large salad, or on drinks at mealtimes.

There is no amount to hit at each sitting; a few mouthfuls more often adds up across a day, and better days can carry more. If you, or someone you look after, are losing weight without trying, or eating has changed suddenly, speak to a GP. My guides to what to eat when appetite is low and high calorie foods for older people go further, and high calorie low volume foods lists the foods that take up least room.

Frequently asked questions

Which food has the highest energy?

Pure fat. The UK food tables list olive oil and groundnut oil at 899 kcal (3,696 kJ) per 100g; nothing goes much higher, because these oils are almost all fat at 9 kcal per gram. Per meal portion, grilled mackerel tops the table above at 396 kcal. My calorie-dense foods guide ranks the rest per 100g.

Are bananas good for energy?

In calorie terms a banana is modest. CoFID gives 81 kcal per 100g, so the BDA's 80g portion is 65 kcal with 16g of carbohydrate, 14g of it sugars. It is easy to eat before or during exercise, and the BDA's sport fact sheet lists two medium-large bananas among its carbohydrate examples, but it adds few calories to a day.

Is dark chocolate good for energy?

It is calorie-dense. CoFID gives plain (dark) chocolate 510 kcal per 100g, with 28g of fat and 63.5g of carbohydrate, so a 20g piece is 102 kcal. The NHS Eatwell Guide puts foods high in fat, salt and sugar in the eat-less-often group, so it suits a long day out better than an afternoon at a desk.

Which fruit has the most energy?

Dried fruit, with most of the water gone: the UK food tables give raisins 256 kcal per 100g and dried dates 235, against 81 for banana, 40 for blueberries and 36 for orange. Avocado is the fresh exception at 171, as most of its calories come from fat. A 30g tablespoon of raisins is 77 kcal; 30g of banana, 24.

Are high energy foods healthy?

It depends on what else they bring and how much you need. The NHS Eatwell Guide wants starchy foods to be just over a third of what we eat, with fats kept to small amounts. If you need more calories for long active days or a small appetite, dense foods help; my guide to how to gain weight covers that.

Sources: NHS, food labels; NHS, calories; NHS, Eatwell Guide; NHS, starchy foods; NHS, sugar; NHS, tiredness; Food information regulation (retained), Annex XIII; Annex XIV; Annex XV; GB nutrition and health claims register; ASA ruling, 13 February 2019; CoFID 2021; BDA, portion sizes; BDA, carbohydrates; BDA, sport and exercise; Cambridge University Hospitals, high energy and protein diet; Asker Jeukendrup, carbohydrate during exercise.