You’re sure to have heard about the keto diet recently – with countless celebs, gym go-ers and self-proclaimed health gurus spruiking its benefits.

But in case you aren’t aware, here’s a quick run-down: a keto diet is very low in carbohydrate, high in fat and moderate in protein. In terms of carbs, you can’t eat much more than the equivalent of a couple slices of bread or a banana per day. Foods that are minimised (or completely off limits) on a ketogenic diet are starchy veg, dairy, legumes, wholegrains and most fruits – all of which are super nutritious.

The theory is that your body shifts from using carbohydrate as its primary source of fuel to fat – and while that sounds rather enticing, I’ve got some reservations. One of my main gripes is that it cuts out entire food groups, which can put you at risk of several nutrient deficiencies. So, to get you up to speed, I’ve outlined some of the key nutrients you could be missing on the keto diet.

1. Fibre

Fibre is key for a healthy gut – but when wholegrains, legumes, and certain fruit and veg are off the menu, it can be hard to get enough. Sure, keto-friendly foods like non-starchy veg, berries, avocado, nuts and seeds all contain fibre, but you’d be unlikely to reach your recommended daily fibre target with these foods alone. FYI, females should aim for 28 grams of fibre per day, while males should aim for 38 grams.

2. Calcium

Strong bones and teeth require a steady supply of calcium, but a glass of dairy milk and a small tub of yoghurt contain about 30 grams of carbs alone (FYI keto diets allow only 20-50 grams of carbohydrate over a whole day). Very careful planning is required to maintain an adequate calcium intake on a keto-friendly diet, including foods like calcium-fortified almond milk, raw almonds with their skin intact or tinned fish with edible bones.

3. Iron

You might be wondering what I’m talking about since meat is allowed on the keto diet, but you might be surprised to learn that grains contribute about a third of the iron in your diet (FYI that’s more than meat does). That’s because grainy foods – like bread and breakfast cereals – can be fortified with iron. What’s more, wholegrain foods naturally contain some iron thanks to their nutrient-rich core. So, remove grains from the diet and you’re cutting out a whole lot of iron, which could leave you feeling lethargic and low in energy. Legumes are another a good source of plant-based iron that you’ll be missing out on as they also aren’t allowed.

4. Magnesium

To get you up to speed, magnesium is a type of electrolyte which works to regulate your body’s biochemistry. Magnesium is also key in muscle and nerve function, and it’s important for the proper formation and structure of bones. Again, grain-type foods are a major contributor, and legumes are an excellent source – but both of these are not allowed on a keto diet. Luckily, nuts and seeds, seafood and spinach are all low-carb options that will give you a boost of magnesium – so be sure to include these on your keto shopping list.

You could be lacking these four key nutrients if you’re following a keto diet, which is where supplements come into play. It’s important to mention that if you’re considering supplementation, you should seek advice from your doctor or dietitian before commencing.

Melissa Meier is a Sydney-based Accredited Practising Dietitian. You can connect with her at www.honestnutrition.com.au or on Instagram @honest_nutrition.

For more on this topic, these are 3 science-backed benefits of the keto diet, and these are the 8 people who shouldn’t try the keto diet.