What is Potassium and why is it needed?
Just like magnesium, potassium is one of the main electrolytes within the body. Along with sodium and chloride, potassium is responsible for maintaining electrolyte balance. Electrolytes are responsible for sending electrical impulses around the body. Specifically, potassium assists in a range of essential bodily functions including: (1).
- Water balance
- Blood pressure control
- Muscle contractions
- Heart rate and rhythm
- pH balance
Normal Ranges in the Body
The average content of potassium in adults is 40-50 mmol (1.6-2.0 g)/kg of body weight (2). Someone who weighs 65 kg would therefore have a level of 2600-3250 mmol in their body.
The concentration of potassium is greater within the intracellular fluid (150 mmol/L) with the remainder in the extracellular fluid (3.5-5.5 mmol/L) (2).
The amount of total potassium is directly related to the level of lean tissue mass. As men generally have greater lean muscle mass, they have a greater level in the body.
Testing of potassium levels is done within the blood. This means it is testing the extracellular fluid and subsequently the normal ranges for the test will be between 3.5-5.5 mmol/L.
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The body cannot naturally produce or make potassium and so it needs to be obtained from the diet.
The recommended intakes vary between America and Europe. In the USA the Adequate Intake (AI) for adults is 4.7 g/day (4700 mg/d) and in Europe, the Reference Nutrient Intake (RNI) is set at 3.5 g/day (3500 mg/d) (3, 4). The lower reference nutrient intake (LRNI/ EMR), is the minimum amount that needs to be met within a day and is set at 2 g/day for adults (3).
As the levels are directly correlated with muscle mass, men may require a slightly higher dose.
Low and High Levels of Potassium
Various hormonal and other factors (including sodium levels), regulate potassium within the body. As with the other electrolytes, it is the role of the kidneys to regulate potassium balance.
Hypokalemia is when the body has low levels of potassium (<3.5 mmol/L). This can cause symptoms including:
- Irregular heart beat
- Muscle weakness or cramping
- Glucose intolerance
- Extreme fatigue
- Constipation, nausea and/or vomiting
Developing such low levels generally should not happen if you are consuming enough potassium in your diet. However, a mild deficiency can be much more common causing symptoms including (5).
- An increase in blood pressure
- Increased salt sensitivity
- Increased risk of kidney stones
- Heart arrhythmias
- Mild muscle cramping
Hyperkalemia is when potassium levels are too high in the body, classed as >7.5 mmol/L (6). This often only occurs when potassium intake exceeds 17.6 g/day which is usually done through supplementation. As well as excessive supplementation, certain medical conditions (such as kidney disease) and medications can cause high potassium levels.
The most common symptom of high potassium is abnormal heart beat. With the severest outcome being that of cardiac arrest (7).
Potassium Levels on a Low Carb Diet
In the first few weeks of starting a low-carb diet, the symptoms of the “keto-flu” can come into full effect. One of the major reasons for the symptoms occurring is due to a change in electrolyte balance. Potassium is one of those electrolytes that can be affected.
In the first few weeks, your body loses a significant amount of water. As this is processed through the kidneys this can then affect the electrolyte balance. Sodium is often the first electrolyte to be lost. Since potassium is closely related to sodium and because the kidneys control the levels, a drop-in potassium can also be experienced.
The symptoms of muscle cramps, heart arrhythmias and fatigue could be a combination of lower salt and subsequent potassium levels.
Therefore, ensuring you get adequate salt in your diet is important both for sodium and potassium balance and to alleviate any keto-flu.
Top 7 Potassium Rich Foods
Below is a list of the top 7 foods high in potassium that you should eat daily to hit your required levels.
All dark green leafy vegetables offer an abundance of nutrients including spinach. One cup (180 g) of cooked spinach offers a significant amount of potassium at 839 mg (24% of RNI) (8). That is almost double what a medium sized banana offers in the way of potassium at only 422 mg!
Although spinach has one of the highest magnesium contents, other dark green leafy veg that offers a good source of magnesium include kale, swiss chard and broccoli.
As well as providing a significant amount of healthy fats, avocados are also packed full of certain electrolytes and minerals.
Just one average avocado (136 g) contains 690 mg (20% RNI) of potassium (9).
Squash is a a great versatile vegetable that also carries with it, a relatively low carbohydrate content at just under 4 g (net carbs) per cup.
It is also relatively high in potassium with one medium zucchini (192 g) providing 512 mg (15%) (10).
Salmon is best known for providing an excellent source of omega 3, but it is also packed full of other essential nutrients. Whilst providing a great source of the B vitamins and vitamin D it is also a good source of potassium. For a 3-oz serving it provides 416 mg (12% RNI) (11).
Other fish including cod, sea bream, monkfish, sardines, herring and mackerel also offer a good source of magnesium.
Often when people look at sources of potassium they list mostly fruits and vegetables but meat sources offer a significant amount of potassium as well. A 4-oz steak provides 384 mg (11% RNI) of potassium (12).
As well as beef, other meats (such as pork and lamb) and poultry (such as chicken and turkey) also offer a good level of magnesium.
Mushrooms make a great base for many low-carbohydrate dishes and can be a great option for those following more of a plant based low-carbohydrate diet. They are known for being higher in vitamin B12 as well as having a great antioxidant capacity which can help fight free radicals (13).
Whilst all mushroom do have a higher potassium level, just 1 cup (72 g) of crimini mushrooms have the highest at 323 mg (9% RNI) (14).
Cauliflower is a cruciferous based vegetable and is extremely nutrient dense, including having a high antioxidant profile in sulfur-containing compounds. One cup (107 g) contains 320 mg of potassium (9% RNI) (15).
Other Sources of Potassium
Nuts and seeds are a great staple within a low carbohydrate diet providing sources of good fats, protein and certain minerals. Almonds offer the highest potassium content out of all the nut options with 1 oz (28 g) providing 200 mg (6% RNI) (16).
Beets are often classed as a superfood as they are packed full of phytonutrients that act as powerful antioxidants. As well as being high in both folate and manganese, it is a great source of potassium. One cup (136 g) provides 442 mg (13% RNI) (17). Since they contain more carbs than other vegetables, they should be eaten in moderation if you follow a low-carb diet.
Due to the risk of developing Hyperkalemia (high potassium levels), supplements are rarely sold with a content of more than 85 mg. Before ever supplementing with potassium, you should always consult with a health professional (18).
To supplement potassium, you can use:
Some people find that supplementing with a small amount of potassium chloride within the day can help with any side effects of low potassium in the diet. A dose of around 20 mEq dissolved in a glass of water and taken with food 1-2 times per day can help with any symptoms of low potassium levels (19). It needs to again be stressed here that if you are unsure of your levels, you must consult a health care professional to recommend on the levels.
Cream of tartar is an ingredient often used in baking and cooking recipes. In itself, it carries a great potassium content with 1/2 teaspoon providing almost 250 mg. This can be a good, natural way to supplement with potassium. However caution must be taken to not over supplement with this as hyperkalemia can occur.
If your low carbohydrate diet is well formulated with foods containing potassium (as listed above) then you should not need to supplement.
However, in the first couple of weeks when you are experiencing keto-flu, the water loss may cause an imbalance in both sodium and potassium. To help with any of the side effects, taking 1-2 teaspoons of lite salt (which is 50% sodium chloride and 50% potassium chloride) per day can be of benefit. If the side effects still persist then adding in the above potassium chloride supplement may also help.
Take Home Message
Potassium is an essential electrolyte which often becomes more essential on a low carbohydrate diet. Ensuring that you get the recommended intake through your diet will make sure that you reach the adequate intake.
If the symptoms of muscle cramping and heart arrhythmia continue then taking in a 1-2 tsp of lite salt per day can help alleviate this. Always be sure to get any blood levels checked before ever supplementing with potassium.
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