Small pile of potatoes

The Vegetable That’s Best Kept in the Dark

Horticulturally, the potato is a vegetable.  It is a type of tuber that grows underground and likes it dark.  If exposed to light, the potato is likely to turn green.  This green is due to chlorophyll forming (the thing that makes leaves green), but it highlights that there are increased toxins in the tuber called glycoalkaloids.  This toxin is actually present in all potatoes but it is not generally harmful as in ‘healthy’ potatoes it is in very low levels and degrades when potatoes are peeled and cooked.   According to the European Food Safety Authority there is “no evidence of health problems associated with repeated or long-term intake of [glycoalkaloids] via potatoes”.  If a potato tastes bitter however, it is better not to eat it.

This toxin is the reason you should not eat potato flowers or the fruit that grows on the upper part of potato plants as the level is significantly higher than in the tuber.  Glycoalkaloids are also present in tomatoes, peppers and aubergine – together the three fruit/veg are referred to as “nightshades”.  Symptoms of glycoalkaloid poisoning include gut irritation, such as nausea and diarrhoea, and drowsiness.  There have been small-scale studies that suggest individuals with irritable bowel disorders (IBD) may be particularly prone to these effects, but evidence is limited.  I would therefore suggest that all individuals monitor their symptoms and remove foods that they find cause irritation rather than eliminating suspected culprits as standard.  For support eliminating foods from your diet, you can of course speak to me as a Nutritional Therapy client.

White Potato Nutrients

Potatoes contain a variety of vitamins and minerals.  They provide good amounts of:

  • Vitamin C – supports collagen production and may therefore support the gut’s barrier function, also an antioxidant that supports the immune system.
  • Potassium – an electrolyte that supports muscle function, including in the digestive system.
  • Vitamin B6 – supports metabolism and may support the gut microbiome.

In lesser amounts white potatoes also provide iron and calcium.  These tubers also provide a small amount of fibre and protein.

They also contain carbohydrate in the form of a quickly digestible starch.

When a Vegetable Isn’t a Vegetable

Nutritionally, potatoes are considered carbohydrates and not vegetables.  They do not count towards your fruit & veg daily intake – they are not part of the traditional “meat and two veg”.  A medium-sized potato (150g) contains around 26g of carbohydrate and it is high on the Glycaemic Index (GI) and is considered to have a high Glycaemic Load (GL).  GI is an indicator of how quickly the sugar in food reaches your blood-stream; the higher the food is placed on the index, the quicker this happens.  GL is used to illustrate to effect of a food on blood sugars by taking account of non-digestible fibres which do not affect blood sugar – again high GL foods have larger impacts on our blood sugar.  High GI and/or GL foods pose a risk of blood-sugar levels spiking and can be a problem for individuals who struggle with blood sugar management, such as those with diabetes.  On the other hand, individuals such as high-intensity athletes, who require quick bursts of energy will find high GI foods helpful before competing.

To slow does the processing of sugars from food into the blood-stream, carbohydrates are best eaten alongside protein, healthful fats.

In the Gut

As already mentioned, potatoes contain nutrients which support gut and our whole body.  But, the carbohydrate can also be great for the gut if the potatoes are cooked and then left to go cold before eating.  This is because the structure of the carbohydrate changes as they cool to a form of resistant starch.  This resistant starch cannot be digested by the body so cold potatoes have less impact on blood sugar levels.  Instead we benefit from it as a prebiotic, a substance that feeds gut bacteria and further supports our health.  Gut bacteria feasting on the resistant starch produce short-chain fatty acids (SCFAs) such as butyrate which helps maintain the gut lining and has anti-inflammatory properties.

It’s About Balance

As you can see potatoes are not inherently bad for us, but they may be a problem for some individuals (consult your doctor or diet adviser before changing your diet if you have been told to limit potatoes and/or carbohydrates!).  The biggest problem we have is portion sizing.  Potatoes are thought of as a staple within the UK and are relatively cheap, they therefore often take centre-stage on our plates.  It is here that the problems lie.

Large amounts of a high GI food puts pressure on the body as the blood sugar raises rapidly requiring large amounts of insulin to be secreted to deal with it.  This puts additional stress on the pancreas (where insulin is produced) and overtime may result in insulin resistance or an inability to produce enough insulin and diabetes.  Furthermore, if we do not use the energy from our carbohydrates we store it as fat, and as you know this can have a wide variety of additional negative effects on the body.  I admit it, I am guilty of eating mashed potato and jacket potatoes in larger portions relative to the rest of my meal than I would boiled potatoes – but I generally make sure I have vegetables, fat and protein with them.  And, I don’t eat them every day!

As with any carbohydrate we should aim to limit our intake to around a quarter of the meal (as a general guide).  This can be a challenge given our culture of basing our meals on the carbs – we often talk about “pasta with…”, “rice with…”, “potatoes with…” instead of thinking about the protein or vegetables first.  Think about how a restaurant menu is written with the carbs as the accompaniment.  This link illustrates the meal balance recommended by BANT, my professional body: .


White potatoes contain several healthful nutrients but in large quantities may contribute to problems with blood sugar management.  It is therefore best to eat them in small amounts and with a selection of vegetables alongside healthy fats and protein.

Potatoes eaten cooked and cooled are also beneficial for the gut and may therefore have a role in reducing inflammation throughout the body.