The ketogenic diet, or keto diet, has become one of the most popular diets in recent years for its ability to enhance fat loss, increase energy, improve athletic performance, and control appetite. But despite these benefits, research and decades of clinical experience have found the diet to increase the risk for multiple nutrient deficiencies. Read on to see what nutrients you should be watching to maximize your health on a ketogenic diet.

What to Monitor on a Keto Diet?

The ketogenic diet is more popular than ever. The diet is extremely low in carbohydrates (usually less than 50 g/day), moderate in protein, and very high in fat. “Ketogenic” refers to the ability of the diet to generate high levels of compounds called ketones that are used as the main energy source instead of glucose. The term was first coined by Dr. Russ Wilder of the Mayo Clinic in 1921, who used the diet to successfully treat epileptic children. However, with the introduction of effective anticonvulsant drugs, the ketogenic, or keto, diet fell out of favor with doctors. It was and still is used to successfully treat epileptic patients who don’t respond to drugs or surgery [1, 2].

The diet has seen a resurgence in popularity in recent decades. Reported benefits range from weight loss and improved blood sugar control to increased energy and mental clarity. Research has backed some of these claims: the keto diet is more effective for weight loss, reducing blood sugar levels, and improving cholesterol and triglycerides than high-protein, calorie-restricted, and even low-fat diets (one RCT of 25 participants, one randomized crossover trial of 17 participants, three RTs of 159 participants) [3, 4, 5, 6, 7].

Beyond weight loss, the diet’s therapeutic potential has also been studied in type 2 diabetes, heart disease, brain trauma, Alzheimer’s disease, and cancer, with promising results [8].

While the diet may have multiple benefits, there are concerns that it can cause multiple nutrient imbalances due to its restriction of carbohydrates and its effects on how the body processes certain nutrients.

Important Nutrients To Monitor

1) Calcium

Calcium is important for bones and teeth, blood vessel function, and muscle and nerve communication [9].

People on long-term keto diets often lose too much calcium in the urine in addition to having acidic urine. High-fat diets can increase the amount of acid generated by the body, which the kidneys must filter out to maintain a stable blood pH. This leads to lower urine pH. Calcium from bones is also used to buffer the increased acid production, leading to higher calcium loss in the urine and lower bone density [10, 11, 12, 13].

In addition, dietary calcium intake may be lower due to the limitation of calcium-rich foods such as fruits, vegetables, dairy, and enriched grains on the diet. Research in rats found that high-fat, low-carbohydrate diets reduced calcium absorption because fats would form indigestible soaps with calcium [14, 15].

Too much calcium in the urine and acidic urine are major risk factors for kidney stones, which is why 3 – 6% of people on a keto diet will develop stones within two years [16].

If a keto diet is something you are doing long-term or often, monitor your kidney health by doing a regular urinalysis. Urinalysis includes test such as urine pH, calcium crystals, and uric acid crystals, which can tell you when you’re at risk of kidney stones.

If you’re on a long-term keto diet, your doctor will often prescribe potassium citrate, which reduces the risk of stones by increasing pH and reducing the loss of calcium in the urine [16, 17].

Keto-friendly foods high calcium include sardines, salmon, spinach, and turnip greens [18].

Because blood calcium is tightly maintained within a narrow range you may need to occasionally check your bone mineral density (z-score, t-score) to determine if you are losing calcium from your bones [9].

2) Selenium

Selenium is a mineral that plays important roles in heart health, reproduction, making thyroid hormones, and protecting the body from oxidative stress [19].

Research and clinical experience in epileptic children on keto diets have found the diet to decrease selenium levels and cause deficiencies in the long run [20, 21, 22].

High-fat foods tend to be low in selenium, which is why keto diets can lead to lower selenium levels [21].

You can easily meet your daily selenium requirement by eating 2-3 Brazil nuts, which are high in fat and low in carbohydrates. Other selenium-rich, low-carbohydrate foods include sardines and shrimp [19].

3) Magnesium

Magnesium is another mineral that has been observed to decrease substantially on a long-term keto diet. This mineral is extremely important for our bodies to produce energy and is required for our nerve cells and brain to function properly. It’s not surprising deficiency has been associated with a wide range of conditions and diseases including Alzheimer’s disease, high blood pressure, type 2 diabetes, heart disease, and migraines [20, 23, 24, 25].

Symptoms of magnesium deficiency include muscle cramps, headaches, anxiety and nervousness, and constipation [25].

Decreased levels seen in people on a keto (low-carb) diet is likely due to eating fewer foods rich in magnesium such as fruits and grains [26, 27, 28, 20].

Magnesium levels can be easily tested and easily corrected. Avocados, almonds, spinach, and salmon are all high in magnesium and low in carbohydrates [29]. Magnesium supplements can also help.

4) Iron

Even though keto diets usually involve eating ample quantities of meat, they also tend to reduce iron levels [30, 13, 31].

Iron is needed for energy production and making red blood cells and a deficiency can cause fatigue and trouble breathing during exercise [32].

Evidence suggests that iron deficiency may develop on the diet due to reduced absorption of iron caused by high amounts of fat [26, 33].

Make sure to check your ferritin levels to see how well your body is storing iron. You can increase your absorption of iron by eating more vitamin C-rich foods such as bell peppers and broccoli (or by supplementing with vitamin C). Also, avoid drinking tea and coffee with meals as these will decrease how much iron your body absorbs [34, 35, 36, 37].

5) Sodium

Sodium is an electrolyte mineral that helps maintain blood volume, pressure, and pH as well as fluid balance in the body [38].

Insulin increases the absorption of sodium by the kidneys and because the keto diet decreases insulin levels, the body releases more sodium than normal [39].

The most common complaints among those just starting out on a keto diet are constipation, headache, muscle cramps, diarrhea, and general weakness. This collection of symptoms is aptly termed the “keto-flu” and is mainly caused by increased sodium, potassium, and water loss (low blood sugar levels also contribute). These symptoms are temporary and usually resolve within weeks [31, 40].

You can reduce these symptoms by increasing your salt intake until your body adjusts to the increased salt loss.

6) Potassium

Like sodium, potassium loss increases during the first couple of weeks on a keto diet and is partly responsible for the flu-like symptoms commonly experienced by new adherents [40, 13].

Potassium helps balance fluids, maintain blood pressure, and helps nerves and muscles communicate. Because it also helps reduce calcium loss in the urine, it is especially important on a keto diet [41, 42, 17].

Spinach, cabbage, parsley, walnuts, hazelnuts, and brazil nuts can help you keep your potassium levels up without kicking you out of ketosis [43].

7) Carnitine

Carnitine is a compound made from amino acids that are found in abundant quantities in the heart and muscles. It helps transport fatty acids to the mitochondria where they are used to make energy. The body can make carnitine, but 75% of our daily requirements comes from the diet (mainly from meat and dairy) [44, 45].

Because carnitine is needed to burn fat, it’s used up much quicker on a keto diet [46].

For most people on a keto diet, carnitine decreases temporarily during the first couple of months. But there is some research that shows deficiency may develop on long-term diets. If this happens, then supplementation becomes necessary to make sure you are burning fat efficiently [47, 48].

If you’ve been on the diet for more than a few months and you’re experiencing fatigue and muscle weakness, this could be a sign you’re low in carnitine. Even if you’re not deficient, supplementing with L-carnitine can improve how well your body burns fats for fuel [49].

You can test your blood carnitine levels to see if you’re low or deficient.

8) Lipids (Cholesterol and Triglycerides)

It’s not surprising that researchers and doctors are concerned about the effects the diet has on cholesterol and triglycerides given the high amounts of fat consumed.

However, multiple studies show that LDL-C, total cholesterol, and triglycerides decrease, and HDL-C increases in overweight and obese individuals on a long-term (>1 year) keto diet (three RTs of 469 total participants and two pilot studies of 132 total participants) [50, 51, 52, 53, 54].

One of these trials found an increase in LDL-C levels (RT of 118 participants) [53].

In a 6-week pilot study in 20 healthy men with normal cholesterol levels, triglycerides decreased but cholesterol levels were unchanged [55].

However, longer trials (>6 months) in epileptic children show the opposite: LDL-C, total cholesterol, and triglycerides increase on a keto diet (four pilot studies of 318 total participants) [56, 57, 58, 59].

It appears that the effect of the keto diet on lipids depends on the health and age of the individual.

Limitations and Caveats

It’s important to note that most of the research examining the effect of the keto diet on nutrient levels has been conducted in children with epilepsy. As children have different nutritional needs than adults, this research may not translate into older, healthy populations.

In addition, there are many variations of the keto diet such as the type of fats consumed (saturated vs. unsaturated), as well as the types of carbohydrates and proteins consumed.

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