Supplement Routine for Fasting Days with Intermittent Fasting

On a fasting day, the question of when each product actually fits sensibly into the day looks different than usual — after all, the usual anchor points provided by several meals are missing. The following suggestion is based on a typical intermittent fasting rhythm with a fasting window followed by an eating window, and explains why each particular timing makes sense.

The Day at a Glance

Morning, in the fasting window: Many people already take electrolytes such as magnesium, potassium, calcium, sodium, and chloride during the fasting window, since products like these are typically formulated to be very low in calories. Whether a specific product fits your chosen fasting approach is best checked using the nutritional information on the pack.

During the fasting window: Going without food for several hours makes adequate fluid intake especially important, and through sweating, or simply through the longer gap between meals, the need for minerals can become noticeable. An electrolyte product can be a practical addition to water during this phase. Unsweetened tea or black coffee are also considered uncritical under most common fasting approaches, but they are not among the supplements discussed here.

If you also train on a fasting day, the order shifts only slightly: with many intermittent fasting approaches, training still takes place within the fasting window or shortly before it, which means electrolytes can, in this case, be timed especially close to the training session. Regardless of that, the fat-soluble vitamins remain tied to the first meal in the eating window.

At the start of the eating window, with the first meal: Fat-soluble vitamins like vitamin D and vitamin K are absorbed better together with a meal that contains some fat than on an empty stomach. The start of the eating window is therefore a good time for a vitamin D3-K2 product, rather than taking it already during the fasting window.

During the eating window: Many people prefer to take magnesium together with a meal, partly because some people find it more unpleasant on an empty stomach. Depending on how the eating window is structured, either the first or a later meal is a good fit for this.

Toward the end of the eating window: Anyone who places their eating window in the early evening can deliberately tie magnesium to the end of the last meal — a time that, for many people, already coincides with the transition into free time and can therefore be built into the daily routine more easily.

Besides the products discussed here, adequate fluid intake is one of the basics of a fasting day — regardless of whether electrolytes are also taken. Anyone who drinks regularly throughout the day generally has an easier time with a longer fasting window than someone who only thinks about adequate fluid intake toward the end of the window.

What matters here is less the exact clock time than the consistency: anyone who places their fasting window and eating window at a similar time each day generally gets used to a fixed structure for taking supplements faster than someone who fasts at completely different times every day.

In summary, this results in a simple basic rule: low-calorie electrolytes fit into the fasting window, while fat-soluble vitamins and magnesium belong in the eating window, ideally with a meal containing some fat. This basic rule can be applied to most common intermittent fasting approaches.

Our Product Recommendations for This Routine

The following three products each cover a different phase of the fasting day: electrolytes for the fasting window, vitamin D3 with K2 for the start of the eating window, and magnesium for later in, or the end of, the eating window. Together they form a simple, easy-to-follow basic setup, without needing to take an unnecessary number of separate products spread across the day.

Electrolyte Complex with Magnesium, Potassium, Calcium, Sodium & Chloride – 360 Tablets

This complex combines magnesium, potassium, calcium, sodium, and chloride in one product. Magnesium contributes to normal muscle function, potassium contributes to the normal function of the nervous system and to normal muscle function, and calcium contributes to normal muscle function.

Since electrolyte products like this are typically very low in calories, many people consider them suitable for use even during the fasting window — it's best to check the nutritional information on the packaging, especially if you follow a strict fasting approach. With 360 tablets per pack, the product is designed for regular use on fasting days and doesn't need to be repurchased for every single fasting day. Shop the electrolyte complex.

The electrolyte complex is especially well suited to longer fasting windows or warmer seasons, when mineral needs tend to be higher. Since the product is dosed tablet by tablet, the amount can easily be adjusted to fasting windows of different lengths, without any measuring or mixing required.

Complex of 4 Bioactive Magnesium Sources – 400mg Elemental Magnesium per Day

Magnesium contributes to normal muscle function, to normal energy-yielding metabolism, and to the reduction of tiredness and fatigue. This complex delivers 400 mg of elemental magnesium per day from four bioactive sources.

Since some people find magnesium unpleasant on an empty stomach, taking it together with a meal in the eating window is the more practical option for many. The four bioactive sources it contains are a quality marker compared with products containing only a single, cheap magnesium compound. Shop the magnesium complex.

The magnesium complex is especially well suited to a regular fasting routine in which the last meal of the day already happens at a fixed time anyway. The four bioactive magnesium sources are a quality marker that makes a noticeable difference regardless of the chosen fasting rhythm.

Vitamin D3 Depot + K2Pure® – High-Dose 5,000 IU, 180 Tablets

Vitamin D contributes to the normal function of the immune system, to the maintenance of normal bones, and to the normal absorption of calcium and phosphorus. Vitamin K contributes to the maintenance of normal bones.

Since both vitamins are fat-soluble, this product should not be taken during the fasted fasting window, but together with the first fat-containing meal in the eating window — which supports absorption. With 180 tablets, one pack lasts a long time for regular fasting days, even with daily use. Shop the Vitamin D3 Depot + K2Pure®.

This product is especially well suited to people who place their eating window mainly in the evening hours, since the fattier main meal usually happens there anyway. With one intake per day, the product can easily be integrated into a single, fixed eating window, without needing several reminders spread across the day.

Staying Flexible

Intermittent fasting is practiced in many different variants, from a daily 16:8 rhythm to less frequent, longer fasting windows. The order suggested here is therefore only a guideline and should be adapted to your own eating window.

With a 14:10 or 16:8 rhythm and a longer eating window, the suggested times can usually be fitted in without much trouble. With shorter eating windows, or less frequent, longer fasting days, it can make sense to bundle all the products more closely together around the first meal, rather than strictly spreading them across the day.

The same logic also applies on days without fasting, such as weekends or vacations: fat-soluble vitamins belong with a meal containing fat, and magnesium fits best in the evening for many people. That way, the routine stays consistent and easy to remember even outside pure fasting days.

As a general rule: intermittent fasting is not equally suitable for everyone, particularly not for pregnant or breastfeeding women or people with certain pre-existing conditions. Anyone taking medication that must be taken regularly or with specific meals should discuss both the fasting itself and the intake of supplements with a doctor or pharmacist beforehand.

If you're unsure where to start: electrolytes are the obvious entry point for the fasting window itself, the Vitamin D3 Depot + K2Pure® belongs at the start of the eating window, and the magnesium complex is easiest to integrate into the last meal of the day. All three together form a well-thought-out basic structure for a typical fasting day, but they can also be used independently of one another.

There's nothing wrong with starting with just one of the three products and gradually expanding the routine once the new fasting rhythm has settled into everyday life. Especially in the first few weeks of intermittent fasting, it's often easier to get used to the changed eating pattern itself first, before adding further habits on top.

Frequently Asked Questions

Do electrolytes break the fast?

That depends on the specific product and the fasting approach you follow. Many electrolyte products are formulated to be very low in calories, which is why many people use them during the fasting window — anyone following a strict approach should check the nutritional information on the pack before taking the product while fasted.

Why shouldn't vitamin D3 + K2 be taken while fasted?

Vitamin D and vitamin K are fat-soluble vitamins that are absorbed better together with a meal containing some fat. That's why the first meal in the eating window is a better fit than the fasted fasting window, in which no fat is typically available.

Is intermittent fasting suitable for everyone?

No. Pregnant and breastfeeding women, and people with certain pre-existing conditions or regular medication use, should consult a doctor before starting a fasting rhythm, since intermittent fasting is not automatically suitable in such situations.

When is the best time to take the magnesium complex?

Many people prefer to take magnesium together with a meal in the eating window, since some people find it unpleasant on an empty stomach. This isn't a strict requirement, though, and anyone who has no issues with it can also take magnesium earlier in the day.

Do I have to follow the suggested order exactly?

No, it's a suggestion meant as guidance. Adjust the timing to your individual eating window and daily life; what matters most is pairing fat-soluble vitamins with a meal rather than taking them fasted, and finding an overall rhythm you can maintain long-term.