Plenty of people who cut carbs feel flat for the first week or two: tired, headachy, light-headed when they stand up, crampy at night. It’s often called “keto flu.” Dr. Stephen Phinney and Dr. Jeff Volek argue that much of it is a mineral problem, and a fairly easy one to fix.
Why cutting carbs changes your mineral needs
When carbohydrate intake drops and insulin falls, the kidneys shift from holding on to sodium to letting it go. Phinney and Volek describe this as the natriuresis of fasting. Water follows, which is part of why early weight loss is so quick. If sodium intake stays low, the body raises aldosterone to conserve it, and that hormone also pushes potassium out. They link the resulting shortfall to fatigue, poor sleep and slow recovery after exercise.
What their research and practice use
In the Virta Health one-year trial of 349 adults with type 2 diabetes, co-authored by Phinney and Volek, participants with headaches, constipation or light-headedness were advised to get adequate sodium and fluid, and those with muscle cramps or twitches were offered a daily magnesium supplement. Blood pressure in the intervention group fell by about 7/4 mmHg over the year. The study was open-label and non-randomized, so it shows the approach is workable, not that the electrolyte advice works on its own.
For most people on a well-formulated ketogenic diet, they suggest roughly 3,000 to 5,000 mg of sodium a day, including about 2 grams from broth or bouillon, potassium from around five servings of non-starchy vegetables, and 300 to 500 mg of magnesium. They are candid that the evidence behind the sodium target rests mostly on small, older studies and observational data.
Balancing it with the broader evidence
That sodium advice sits well above Health Canada’s guidance to stay under 2,300 mg a day; the average Canadian already takes in about 2,760 mg. Public guidance is written for a typical diet heavy in processed food; the low-carb advice is for people whose kidneys are actively shedding sodium. If you aren’t genuinely low-carb, extra salt isn’t for you.
For magnesium, the wider evidence is reassuring but modest. A meta-analysis of 34 randomized, placebo-controlled trials found that a median 368 mg a day for about three months lowered blood pressure by roughly 2 mmHg systolic and 1.8 mmHg diastolic. The U.S. National Institutes of Health sets the upper limit for supplemental magnesium at 350 mg a day for adults, largely because higher doses commonly cause diarrhea.
How to apply it
- Consider extra sodium only if you are following a true low-carb or ketogenic plan.
- Feeling flat early on? Try a daily cup of salted broth or bouillon before blaming the diet.
- Get potassium from food: non-starchy vegetables at most meals.
- For night cramps, a magnesium supplement may help. Stay at or under 350 mg from supplements unless your physician advises otherwise.
- If you have high blood pressure, heart or kidney disease, or take diuretics or blood pressure medication, check with your physician first. Phinney and Volek themselves advise staying at or under 3,000 mg of sodium with high blood pressure or diuretic use.
Want a low-carb plan that leaves you energized instead of drained? The Longevity Path coaching team would love to help.
References
- Phinney S, Volek J. Sodium, nutritional ketosis, keto flu and adrenal function. Virta Health. 2017 (updated 2026). https://www.google.com/url?q=https://www.virtahealth.com/blog/sodium-nutritional-ketosis-keto-flu-adrenal-function&source=gmail&ust=1794266173669000&sa=E
- Phinney S and the Virta Team. How much sodium, potassium and magnesium should I have on a ketogenic diet? Virta Health. 2025. https://www.google.com/url?q=https://www.virtahealth.com/blog/sodium-potassium-magnesium-ketogenic-diet&source=gmail&ust=1794266173669000&sa=E
- Hallberg SJ, McKenzie AL, Williams PT, et al., including Phinney SD and Volek JS. Effectiveness and safety of a novel care model for the management of type 2 diabetes at 1 year: an open-label, non-randomized, controlled study. Diabetes Therapy. 2018;9:583-612. https://www.google.com/url?q=https://doi.org/10.1007/s13300-018-0373-9&source=gmail&ust=1794266173669000&sa=E
- Health Canada. Sodium intake of Canadians in 2017. Government of Canada. 2018. https://www.google.com/url?q=https://www.canada.ca/en/health-canada/services/publications/food-nutrition/sodium-intake-canadians-2017.html&source=gmail&ust=1794266173669000&sa=E
- Zhang X, Li Y, Del Gobbo LC, et al. Effects of magnesium supplementation on blood pressure: a meta-analysis of randomized double-blind placebo-controlled trials. Hypertension. 2016;68(2):324-333. https://www.google.com/url?q=https://doi.org/10.1161/HYPERTENSIONAHA.116.07664&source=gmail&ust=1794266173669000&sa=E
- National Institutes of Health, Office of Dietary Supplements. Magnesium: fact sheet for health professionals. 2026. https://www.google.com/url?q=https://ods.od.nih.gov/factsheets/Magnesium-HealthProfessional/&source=gmail&ust=1794266173669000&sa=E
