Whether you consider tomatoes to be fruits or vegetables may be a controversial topic, but for those sticking to a ketogenic diet, the answer doesn’t really make a difference. While fruits have a reputation for being high in sugar (and therefore carbs), there are also plenty of high-carb vegetables that will throw off your macros just as easily.
Achieving ketosis involves careful planning and calculation, sticking to a strict low-carb and high-fat ratio. You’ll be happy to know that 100g of tomato contains only 2g to 3g of net carbs, ten times less than most fruits. That’s around 4.7g per medium tomato.
While keto communities can’t quite agree whether this makes tomatoes a low-carb or high-carb food, the most important thing is to keep the quantities in mind. It’s very feasible for tomatoes to fit into your daily macros, and the nutritional benefits are well worth the effort.
But what about those handy tinned tomatoes you can pick up in the supermarket? For most families, canned tomatoes are a pantry staple, used to make endless sauces, soups and curries. So when you’re trying to cook keto-friendly meals, it’s important to know how the macros of tinned tomatoes compare to fresh tomatoes.
Canned tomatoes have around 4.6g of net carbs per 100g and fresh tomatoes have 2g to 3g. Store-bought tomato-based products, including pasta sauces, tomato paste and canned tomatoes, may contain added sugars, so always check the ingredients list to avoid these high-carb varieties.
Keen to find out more about tomatoes on a keto diet? Read on to dive into the nutrition of fresh and canned tomatoes, plus handy ways to substitute one for the other.
How Many Carbs Are In Canned Tomatoes?
The carbohydrate count of canned tomato products depends on the manufacturer and the way the tomatoes are prepared, as the ratio of juice to tomato and varieties of fruit makes a difference. Tinned tomatoes vary from whole, crushed and diced tomatoes to more processed products like tomato paste, tomato puree and tomato sauces.
Here are the approximate values for each variety:
(per 100g)
· Whole peeled canned tomatoes: 5g carbs
· Crushed tomatoes: 4g to 8g carbs
· Diced tomatoes: 4g to 5g carbs
· Stewed tomatoes: 5g to 9g carbs
· Tomato paste: 18g carbs
· Tomato sauce: 5g to 7g carbs
· Tomato puree: 9g to 13g carbs
Tinned tomatoes are not necessarily inferior to the fresh ones when it comes to nutrition, but it’s the potential for added ingredients – especially sugar and sweetened tomato paste – that make these products less keto friendly.
Luckily, it’s not common for canned tomatoes – such as plain diced and crushed tomatoes – to contain added sugar in Australia. More processed options such as tomato paste and jarred tomato sauce are where the dangers lie, since sugar is almost always added to these tomato products.
Nutrition of Canned Tomatoes vs Fresh Tomatoes
Most of us assume that fresh is best and anything in a can will always be a little bit less nutritious. However, this myth is thoroughly busted when it comes to tomatoes! They contain a phytochemical or antioxidant called lycopene, which is what gives tomatoes their bright red colour. Like many antioxidants, lycopene is known to play a role in preventing cancer, reducing inflammation, preventing heart disease and protecting skin from sun damage.
Studies have demonstrated that lycopene is even more bioavailable in canned tomatoes than fresh tomatoes. The cooking process opens up cell walls in the tomato and allows the lycopene to be more readily absorbed into our body. The amount of calcium and iron is also three times higher in canned tomatoes compared to fresh tomatoes.
When it comes to other nutrients, though, fresh tomatoes have a higher quantity of vitamins A and K and also folate. Both fresh and canned tomatoes are rich sources of antioxidants like beta-carotene, lycopene, lutein and zeaxanthin. Beta-carotene, lutein and zeaxanthin levels are higher in raw tomatoes.
In more good news, tomatoes are a great source of fibre, vitamin C and potassium, regardless of whether they’re fresh or canned.
What About BPA in Canned Tomatoes?
BPA has certainly gotten a lot of attention over the past 10 years, and it’s now making the list of substances more health-conscious individuals try to avoid. Traditionally, cans are manufactured with BPA or Bisphenol A, a compound used to make plastics and resins. BPA is suggested to have hormone-disrupting effects on the body, potentially affecting healthy development and reproductive health.
Acidic foods like canned tomatoes are singled out as a concern because the high acidity levels make BPA leaching more likely. After widespread publicity, many tinned tomato brands are now BPA- free.
If you’d still prefer to avoid tinned food, find out below how you can substitute fresh tomatoes for the canned variety or make your own tinned tomatoes at home, stored safely in glass jars.
Substituting Canned Tomatoes For Fresh Tomatoes
If a recipe calls for fresh tomatoes and you’ve just discovered yours have gone bad, you may want to know whether you can use canned tomatoes as a replacement. Chopping up tomatoes also involves a lot of effort and mess, so you may just be looking for a quick shortcut to get dinner on the table sooner.
You can substitute canned tomatoes for fresh tomatoes, depending on the recipe – naturally, it won’t work as well for a ham-and-tomato sandwich as it does for a pasta sauce. If the tomatoes are meant to be chopped and cooked, though, there’s a good chance the canned variety will work as a substitute. It’s best to choose whole peeled tomatoes when you substitute canned for fresh – that way you can easily use the same quantities, and you can include as much or as little of the juice as you prefer.
If you are following a recipe and it has precise quantities, you can figure out the equivalent amount of canned tomatoes to substitute. Most brands of canned tomatoes come in 400g and 800g tins, which includes the weight of the juice as well as the tomatoes themselves. An 800g tin contains around 10 to 12 tomatoes, while a smaller 400g can contains 5 to 6 tomatoes.
Substituting Fresh Tomatoes For Canned Tomatoes
Canned tomatoes are convenient to keep on hand, but if you’ve got an excess of fresh tomatoes lying around, you might as well use them as a substitute. You can always make your own canned tomatoes at home (see the instructions below), but if you’re looking to use them immediately, you can just swap the canned tomatoes in your recipe for fresh ones.
You’ll have to consider a few key differences, though: you may need to allow extra cooking time for your tomatoes to soften, and canned tomatoes often have more juice in them than fresh tomatoes, too. You can definitely make up the difference with water or stock if you find the recipe needs more liquid.
It’s up to you whether you’d like to peel your fresh tomatoes before chopping or if you don’t mind the texture of the tomato skins in your dish.
You can typically substitute 2 cups of fresh tomatoes for one 400g can of canned tomatoes. A 400g can of tomatoes may have 5 to 6 small tomatoes in it, but measuring by cups means it doesn’t matter what size or variety your tomatoes are.
DIY Canned Tomatoes Recipe
If you’ve picked up a bumper crop of tomatoes at the markets, why not try canning your own tomatoes at home? Not only does it save those tomatoes from decomposing in your fridge, it also means you can control what ingredients are added. Preserving your own tomatoes in glass jars also avoids the BPA that can be found in some canned foods.
With a few simple steps, you can transform fresh tomatoes into convenient DIY tinned tomatoes ready for use in sauces, soups and stews. The ingredients are very simple – just tomatoes and salt for a basic recipe. You can also experiment with adding herbs like oregano and basil, perfect for use later in Bolognese and other Italian dishes.
You can reuse any jars lying around your kitchen to can your tomatoes, as long as you clean them thoroughly and then sterilise the jars before use. This is easy to do using the oven, stovetop, or even in the dishwasher, so don’t let this step intimidate you too much.
The tomatoes should be consumed within a year, but given how handy tomatoes are in the kitchen, I’d be surprised if you didn’t find a use for them much sooner! You can also freeze your prepared tomatoes if you’re using a freezer-safe container to store them.
Low Carb Canned Tomato Products
When it comes to simple canned tomato products – such as crushed, diced or pureed tomatoes without flavourings – most brands in Australia are relatively low carb. If the ingredients list doesn’t indicate there’s anything else added, that’s really as low carb as it’s possible to get.
If you’re looking to reduce the carb count further, you can minimise the amount of tomato that ends up in the portion you eat. Many recipes can be padded out with extra stock, while adding additional herbs and spices will help make up for the weaker tomato flavour.
Carbohydrates in some canned tomatoes in Australia:
(per 100g)
· Coles Homebrand Chopped Tomatoes: 3g of carbs
· Woolworths Essentials Diced Tomatoes: 3.3g of carbs
· Coles Organic Diced Tomatoes: 3.4g of carbs
· Annalisa BPA Free Diced Tomatoes: 3.8g of carbs
· Annalisa Organic Diced Tomatoes: 3.6g of carbs
· Mutti Pulpa Diced Tomatoes: 3.9g of carbs
· Coles Diced Australian Tomatoes: 4.3g of carbs
· Ardmona Rich & Thick Tomatoes: 5.3g of carbs
· Ardmona Crushed Tomatoes: 5.3g of carbs
· Ardmona Crushed Vine Ripened Tomatoes: 6.9g of carbs
When it comes to low carb tomato pastes and sauces, look for options that only contain tomatoes, herbs and spices, without added sugar. Tomato paste will inevitably be higher in carbs as it’s much more concentrated, but a little bit goes a long way in any recipe.
For lower carb pasta sauce, Keep It Cleaner is a popular option that’s easy to find in Australian supermarkets. You can also make your own pasta sauce, pizza sauce and even tomato sauce at home using canned tomatoes as a base. If it needs some additional sweetness, keto sweeteners work well to balance the flavour without adding carbohydrates.
Related Questions
How many carbs are there in cherry tomatoes?
Cherry tomatoes are a very popular small variety of tomato. Cherry tomatoes contain 3.6g of carbohydrates per 100g, or 6g of carbs per cup. One cherry tomato has 0.67 g of carbs.
Are onions keto friendly?
Onions can be eaten in moderation on a keto diet. Onions do not have any natural fat content and mostly contain carbohydrates. An average onion contains 0 g of fat, 14 g of carbs, and 2g of protein. However, serving sizes are usually small: half a cup of cooked onion has 2.68g of net carbs.
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