Therapeutic Fasting and Side Effects: Understanding the Adjustment Days

Key points at a glance

• Side effects such as weakness, shakiness, nausea, headaches or feeling cold belong to the adjustment days, in which the metabolism switches to fat burning.
• In the large 2019 PLOS One study of more than 1,400 medically supervised fasters, adverse effects occurred in fewer than one per cent; the mild side effects showed mainly in the first few days and subsided on their own or with simple measures.
• A more pronounced fasting crisis is the exception and can be recognised and caught early under medical supervision.
• Proven measures are a green tea with honey, enough fluid and warmth; the medical team adjusts pace, duration and supervision individually.
• At the Tannerhof, therapeutic fasting is always medically supervised; in case of uncertainty, a telephone medical pre-consultation can be requested before arrival.

What happens during the adjustment days

Fasting after Buchinger is the conscious, time-limited abstention from solid food and stimulants. As soon as the quickly available carbohydrate stores decline, the metabolism switches within the first few days from glucose to fatty acids and ketone bodies. It is precisely in this transitional phase, on the second and third fasting day, that temporary side effects can arise — the body reorganises its energy supply, and that is noticeable for a few days.

These side effects are a known and well-described part of fasting. For guests who would like to look calmly at a medically supervised fasting programme, Body Detox is the right programme page; the method itself is set out on the page on fasting after Buchinger. What follows first is what can occur during the adjustment days, and then how the medical supervision at the Tannerhof carries this phase.

To place the frequency in context, the data help. The large observational study by Wilhelmi de Toledo and colleagues, published in PLOS One in 2019, followed more than 1,400 people over fasting periods of four to twenty-one days after the Buchinger method. Under this daily clinical supervision, adverse effects occurred in fewer than one per cent of participants, and severe or lasting events did not occur. The milder side effects showed mainly in the first fasting days and subsided on their own or with simple measures. This study and the guidelines on fasting therapy that can be consulted at the Medical Society for Fasting and Nutrition (ÄGHE) carry the following sections.

Possible side effects at a glance

During the adjustment days, the effects that can arise are above all those connected with the briefly fluctuating blood sugar and the metabolic changeover. In the PLOS One study, slight changes in sleep were among the most frequently named observations, followed by headaches, muscle complaints and temporarily low blood sugar — throughout described as mild and temporary. Typical of the adjustment days are:

• Weakness and tiredness, because the body is changing how it produces energy.
• Shakiness and a feeling of inner restlessness with briefly low blood sugar.
• Nausea, usually mild and temporary.
• Headaches, often in the first one or two days.
• Feeling cold, because the resting metabolism produces less heat.
• Slight changes in sleep, often with lighter sleep overall.

As a rule these effects are harmless and belong to the transition. In the study they disappeared spontaneously or with simple, natural measures, without the fast having to be interrupted. The ÄGHE too describes that any initial disturbances of well-being are usually followed by a phase of well-being and a brightening of mood — the changeover is a passage, not a permanent state.

The fasting crisis explained factually

The term fasting crisis means a more pronounced clustering of the adjustment effects, for instance when headaches, weakness, nausea or circulatory fluctuations come together and become more noticeable. It typically appears in the early adjustment phase and is an expression of the same transition, only stronger. Often the fluid and mineral balance plays a part, as does too quick a start without sufficient relief beforehand.

Under medical supervision, a pronounced fasting crisis is the exception. The favourable safety profile of the PLOS One study — adverse effects in fewer than one per cent, no severe or lasting events — rests precisely on the fact that people were assessed beforehand and supervised daily during the fast. This is exactly where the value of supervision lies: changes are noticed early, and the pace can be adjusted before a side effect becomes more than that.

How medical supervision catches the changeover

At the Naturhotel Tannerhof, therapeutic fasting is always medically supervised — that is the attitude of the house, grown over three medical generations. The doctors at the Tannerhof are experts in fasting, and the adjustment days are precisely the phase in which this experience carries. Wherever a medical statement appears in this text, it is either supported by the guidelines and studies on fasting therapy that can be consulted at the ÄGHE, or it describes the medically supervised practice at the Tannerhof.

Much can be caught with simple, proven measures. A green tea with honey balances a brief dip in blood sugar without leaving the character of the fast behind — a spoon of honey or an espresso is expressly allowed as a small concession. These include:

• Green tea with honey to bridge a low point.
• Plenty of fluid, around three litres a day, as fasting tea, mineral water, lemon water or hot ginger water.
• Warmth against feeling cold — a bathrobe and hot-water bottle are part of the standard equipment in the room at the Tannerhof.
• A base preparation if needed, against acidic metabolic products and uric-acid crystals.
• Measured movement and rest in the right balance, matched to the day.
• Adjustment of pace and duration by the medical team, where it makes sense.

The medical appointments form a calm arc. At the start there is the intake consultation on the first fasting day, conceived holistically with history-taking, physical examination including bioimpedance analysis to measure body composition and a review of medications — and beyond that, the questions of why you are fasting, what is happening in your life right now and what previous fasting experience you bring. The length of stay is booked before arrival; from the intake consultation onward, the course and supervision can be agreed together with the medical team and adjusted if needed. If needed, an interim discussion follows, and at the end there is a closing discussion to evaluate the change. Every person is different, and the individual stands at the centre.

Why good preparation makes the changeover gentler

The adjustment days can be cushioned before they begin. A fasting week does not start with the first soup: before arrival, the doctors at the Tannerhof recommend one or more relief days at home, for instance a fruit, potato, vegetable or raw-food day. How many there are is for the guest to decide. This gentle run-up gives the metabolism time to settle into the abstention and takes some of the force out of the transition.

In the house itself, too, the setting is laid out for the changeover. The accompanying treatments are deliberately broad and tailored directly to fasting. They include the medical history-taking and examination, the medical follow-up consultation and the closing discussion, bioimpedance analysis and, depending on the programme, IHHT altitude training, the Kneipp alternating affusion and magnesium-rich detox baths, the liver-supporting hayflower compress, aroma compresses as well as mud and warm packs, the fasting massage, the detox massage with Königsöl or the acidosis massage, lymphatic drainage and foot reflexology, breathing therapy and sauna sessions. Some of these treatments warm and relax precisely during the adjustment days, others support the metabolism. For the mental side there is psychotherapeutic coaching, nature coaching, business and communication coaching and art therapy.

Movement remains part of the fast, only measured in moderate doses: moderate base endurance training and moderate strength training, a hike or a sauna session at a pace that suits fasting. Summit tours and running are possible, only slower than in everyday eating life — the body feeds itself from within. Fasting guests take their meals in the Fasterstube, the dining room reserved for them, and experience with fasting is anchored throughout the house, from reception through the restaurant to the therapists. So the changeover does not become a hurdle one takes alone but a phase that is carried.

What comes after the changeover

After the adjustment days, the experience often changes markedly. Many fasters report a growing lightness, a clearer head and better well-being — in the PLOS One study, physical and emotional well-being rose in all groups, and more than ninety per cent of participants experienced no hunger during the fast. Some people experience a fasting euphoria through the altered serotonin metabolism, varying from person to person. Often the need for sleep decreases while sleep itself grows lighter.

So the transition belongs to the whole. Fasting after Buchinger is more than a diet and not primarily a method for losing weight — it is a therapeutic method, a cleansing on many levels and an encounter with oneself. The body works on two levels at once: it switches to fat burning, and it begins autophagy, the body's own recycling and cleansing processes at the cellular level. The adjustment days are the entrance to this effect, not its price. Over it all lies the place: Bayrischzell, the alpine meadow, the mountain brook, clear and pure mountain air and the view towards the Wendelstein. Mein Versteck in den Bergen – my hideaway in the mountains – is the calm setting in which fasting and medical supervision amplify each other.

Anyone wishing to see the concrete framework and book it online will find it in the Body Detox programme. In case of uncertainty before arrival — for instance with a chronic illness or ongoing medication — a telephone medical pre-consultation can be arranged on request. An overview of therapeutic fasting and the Schlanke Tanne Low Carb, the house's own low-carb way of eating, is given by the Therapeutic Fasting and Schlanke Tanne hub.