Introduction
Starting keto usually comes with high hopes. Then, in the first week or two, many people hit an unexpected wall: headaches, low energy, brain fog, leg cramps at night. It feels like coming down with the flu. This is what people call keto flu.
It is not the flu, and it does not mean keto is wrong for you. Most of the time it is a sign that your electrolytes have fallen behind. This guide explains why keto flu happens and gives you a complete plan: salt, magnesium and a solid daily nutrition foundation.
Common Keto Flu Symptoms
A 2020 study in Frontiers in Nutrition collected first-hand reports from people on keto in online forums. The most common symptoms were:
- General flu-like feelings
- Headache and dizziness
- Fatigue and low energy
- Trouble concentrating ("brain fog")
- Stomach discomfort and nausea
- A change in how the heartbeat feels
Symptoms usually peaked in the first week and had passed by about week four. In other words, this is a transition period while your body switches fuel sources. With the right preparation, it can be far smoother.
Why It Happens: Sodium and Water Loss
When you cut carbohydrates sharply, insulin falls. One of insulin's jobs is to help the kidneys hold on to sodium. As insulin drops, the kidneys excrete more sodium, and water goes with it. This is called the natriuresis of nutritional ketosis. At the same time, glycogen stored in the liver and muscles is used up, releasing the water bound to it.
A 2023 study in the Journal of Clinical Endocrinology & Metabolism notes that if the extra sodium lost on a ketogenic diet is not replaced, circulating volume falls, which can lead to dizziness, fatigue and weakness. That is a close match for keto flu.
There is another factor that often gets overlooked: magnesium. Keto cuts out whole grains, legumes and much of the fruit people usually eat, and these are important dietary sources of magnesium. Magnesium takes part in more than 300 enzyme reactions and supports normal muscle and nerve function. Low magnesium intake is a common contributor to night-time cramps.
The Plan: Water, Salt and Magnesium
1. Drink enough water
You lose water along with sodium, and you may not feel thirsty at first. Drink on a schedule and aim for pale yellow urine.
2. Add salt
Sodium is the electrolyte you most need to replace early on keto. Simple ways to do it:
- Have a cup or two of broth or bone broth each day.
- Salt your food generously rather than aiming for low salt.
- If you feel dizzy or drained, try a glass of lightly salted water first.
In the 2023 study above, one ketogenic group ate considerably more sodium than general dietary guidelines suggest, and the researchers noted that this may be needed to offset the sodium-losing effect of keto. Needs vary from person to person; if you have high blood pressure or kidney problems, or take blood pressure medication, talk to your doctor before changing your salt intake.
3. Top up magnesium: USANA MagneCal D
Nuts, seeds, avocado and dark leafy greens are keto-friendly magnesium sources. On top of food, a supplement is the simplest way to keep magnesium steady.
USANA MagneCal D uses a 1:1 calcium-to-magnesium formula. On the Australia/New Zealand label, each tablet provides 125 mg magnesium and 125 mg calcium, plus vitamin D3, in citrate and carbonate forms that are well absorbed and gentle on the stomach. The adult directions are two tablets twice daily with food, providing 500 mg of magnesium a day.
Magnesium supports normal muscle contraction and relaxation, the nervous system and energy metabolism; ATP, the cell's energy molecule, has to bind to magnesium to be biologically active. That is exactly the support a body adapting to keto needs. If you are new to magnesium supplements, you can start with a lower dose and build up to the label directions.
MagneCal D is NSF Certified for Sport. Learn more: USANA MagneCal D and the 1:1 formula.
🎬 Watch the video: USANA MagneCal D: The Best Calcium-Magnesium Balance Formula
4. Build your daily foundation: USANA CellSentials
Cutting carbs also means less fruit, whole grains and legumes, which are major sources of B vitamins, vitamin C and many minerals. B vitamins help turn fat and protein into energy, the very pathways keto relies on.
USANA CellSentials is a two-bottle system, Vita-Antioxidant and Core Minerals, with USANA's US-patented InCelligence Complex. USANA describes it as comprehensive, optimised foundational nutrition with powerful antioxidant protection that supports cellular renewal. Take two tablets of each twice daily with meals.
Whatever way you eat, your nutrition foundation comes first. Both CellSentials products are NSF Certified for Sport. Learn more: How to Take USANA CellSentials.
🎬 Watch the video: USANA CellSentials vs a Regular Multivitamin: What's Different
5. Lower carbs gradually
If symptoms are strong, consider reducing carbs over one to two weeks instead of dropping to your target overnight. Giving your body time to adapt makes the transition much smoother.
Your First-Month Keto Plan
| Need | What to do / USANA product | How |
|---|---|---|
| Fluids | Drink on a schedule | Aim for pale yellow urine |
| Sodium | Broth, bone broth, salt your food | A cup or two of broth daily |
| Magnesium | MagneCal D | Two tablets twice daily with food (AU/NZ label) |
| Daily foundation | CellSentials | Two of each, twice daily with meals |
Starter plan: water + salt + MagneCal D, aimed squarely at the early-keto electrolyte gap.
Complete plan: add CellSentials to fill the nutrition gaps left by less fruit, grains and legumes, and keep it going long term.
Formulas and directions differ by country; always follow the label on your product.
Fasting? The Same Plan Applies
Intermittent and extended fasting also lower insulin and increase sodium loss, so dizziness, fatigue and cramps are common there too. The principles are the same: water and salt during the fast; MagneCal D and CellSentials with meals inside your eating window.
Why USANA
- Pharmaceutical-grade manufacturing. USANA manufactures its supplements to pharmaceutical-grade standards, testing every batch for purity, identity, composition, potency and safety.
- NSF certification. MagneCal D, CellSentials and other products, ten US products in all, are listed in the NSF Certified for Sport database. USANA also holds NSF/ANSI 173 (dietary supplement contents) and NSF/ANSI 455-2 (dietary supplement GMP) certification.
- More than 30 years of science. USANA was founded by a scientist in 1992, has more than 150 scientists and is listed on the New York Stock Exchange.
Learn more: The USANA Difference.
What to Read Next
- Why the calcium-to-magnesium ratio matters → USANA MagneCal D
- Daily foundation nutrition → How to Take USANA CellSentials
- Recovering after training → Supplements for Muscle Recovery
- 📄 USANA prices in your country, member vs retail: Price list
References
- Bostock ECS, et al. Consumer Reports of "Keto Flu" Associated With the Ketogenic Diet. Front Nutr. 2020;7:20.
- Belany P, et al. Effects of Hypocaloric Low-Fat, Ketogenic, and Ketogenic and Ketone Supplement Diets on Aldosterone and Renin. J Clin Endocrinol Metab. 2023;108(7):1727–1739.
Important Notice
This article is general information about dietary supplements, written by an independent USANA Brand Partner. It is not medical or nutritional advice. A ketogenic diet is not right for everyone: if you take medication for blood sugar or blood pressure, have kidney or heart problems, or are pregnant or breastfeeding, talk to your doctor before starting keto or changing your salt or supplement intake. Product formulas, directions and availability differ by country; always read the label on your product and use as directed. These statements have not been evaluated by the Food and Drug Administration, and USANA products are not intended to diagnose, treat, cure or prevent any disease.
