Therapeutic Fasting: Effects & Autophagy — What Happens in the Body

Key takeaways

• Therapeutic fasting works on two clearly separate levels: fat burning with ketosis on one side, autophagy on the other.
• The metabolic switch from glucose to fatty acids and ketone bodies sets in after roughly 24 to 72 hours (as described in the study literature).
• Autophagy is the medical term for cellular recycling — put more plainly: cleaning happens everywhere, all recycling processes are driven forward.
• Mentally, fasting days create a caesura; sleep needs often drop while sleep becomes lighter, and a fasting euphoria can occur.
• For certain chronic and metabolic conditions, fasting can be medically relevant (guidelines and studies available from the ÄGHE) — always under medical supervision.

What the effect of therapeutic fasting consists of

Therapeutic fasting after Buchinger is the conscious, time-limited abstention from solid food and stimulants. It is not a zero diet and not primarily a weight-loss method, but a therapeutic method, cleansing on many levels and an encounter with oneself. The question carrying this article is a different one from how it proceeds or which method is used: what actually happens in the body when solid food falls away for a few days?

The short answer is that two things happen at the same time, things that tend to get lumped together. The body re-covers its energy needs, and it tidies up at the level of the cells. The first is fat burning with the transition into ketosis, the second is autophagy. Both belong to fasting but describe different mechanisms — and exactly this distinction makes it clear why fasting is more than losing weight. Anyone wanting to see the medically supervised framework will find it in the Body Detox programme, embedded in the Therapeutic Fasting and Schlanke Tanne hub.

At Naturhotel Tannerhof this effect has been part of the house's practice for over 70 years, medically supervised across three generations of doctors. Every statement in this text is either backed by guidelines and studies on fasting therapy available from the Society of Doctors for Fasting and Nutrition (ÄGHE), or it describes the medically supervised practice at the Tannerhof.

The two levels of effect at a glance

Before each level is addressed on its own, a comparison helps. It shows that fat burning and autophagy are not the same thing, but two processes running in parallel during fasting.

Both levels occur together during fasting. Summarising them as a single mechanism would short-change the effect. That is why they stand here one after the other, each on its own.

First level: fat burning and the path into ketosis

The first level is the energetic one. As long as solid food is supplied, the body draws its energy predominantly from carbohydrates, that is, from glucose. During fasting the quickly available carbohydrate stores recede, and metabolism switches over: away from glucose, towards fatty acids and the ketone bodies formed from them. This is the side of fasting on which the body increasingly lives from its own reserves.

This switch is well described. In their review article in the New England Journal of Medicine in 2019, Rafael de Cabo and Mark P. Mattson classify precisely this process as the metabolic switch: the organism moves from glucose-based energy generation to a ketone-based one as soon as the rapidly available sugar stores are used up. The authors describe that this transition typically sets in some hours to days into a fasting phase and is accompanied by a series of adaptive cellular responses. For multi-day therapeutic fasting this means: the switch to fat burning and ketone bodies lies in the order of roughly 24 to 72 hours after the start of fasting.

How this ketosis behaves over a longer fasting period is shown by a large observational study by Wilhelmi de Toledo and colleagues from 2019, published in PLOS One. It accompanied 1,422 people over fasting periods of four to twenty-one days following the Buchinger method. The transition into ketosis could be documented there through rising ketone bodies, which reached a plateau after about five days — a measurable indication that the body has switched stably to generating energy from fat. That weight drops in the process is a side effect of this level, not its actual purpose.

Second level: autophagy, the cellular recycling

The second level does not mean fat burning but the body's own recycling and cleansing processes at the cellular level. Autophagy — literally the self-digestion of the cell — is the established medical term for it: cell components are broken down, reused and reordered. Described more nicely: all recycling processes are driven forward, cleaning happens everywhere. This occurs not just in one place, but on many levels — cellular, vascular, in connective tissue, the gut, the brain, liver and kidneys.

How fundamental this mechanism is for the life of the cell is shown by the Nobel Prize in Physiology or Medicine 2016. It went to the Japanese cell biologist Yoshinori Ohsumi for the discovery of the mechanisms of autophagy. In the 1990s Ohsumi had made visible, in yeast cells, how the cell encloses its own components in small vesicles, transports them to its recycling stations and dismantles them there in order to reuse the building blocks. This research turned a long-suspected process into a precisely described one — and it explains why fasting medicine devotes so much attention to autophagy.

What remains important is the separation of the two levels. Fat burning answers the question of where the body takes its energy from during fasting. Autophagy describes what happens in the cells in terms of order and renewal. Both run together during fasting, yet they are not the same event. At the Tannerhof, autophagy is the actual aim of fasting, medically substantiated and positively describable as the great tidying-up in the body.

The mental side: caesura, sleep and fasting euphoria

The effect of fasting involves more than metabolism. Mentally, fasting days create a caesura and an abundance of time with and for oneself. Eating is reduced to the essentials, and with it a good part of everyday routine falls away — a counterpole to sensory overload and constant acceleration.

Two observations frequently recur here, both differing individually in how pronounced they are:

• Sleep. Sleep needs often decrease, while sleep becomes lighter at the same time. Some people wake earlier and more clearly during fasting without feeling under-rested.
• Fasting euphoria. Some experience an elevated, light mood over the course of the fasting days. It is attributed to the altered serotonin metabolism and does not occur in everyone, nor to the same degree.

These mental effects are not a promise but a frequent experience that the medical team at the Tannerhof knows from accompanying many fasting weeks. For the mental side, the house also offers psychotherapeutic coaching, nature coaching, business and communication coaching as well as art therapy — fasting is, after all, more than a change of diet for a few days.

When fasting becomes medically relevant

From the two physical levels and the mental side it follows why fasting can be medically relevant for certain conditions. The guidelines on fasting therapy come from the Society of Doctors for Fasting and Nutrition (ÄGHE); further studies on fasting therapy are available there. Under professional supervision, they classify the use of therapeutic fasting in areas including:

• Rheumatic diseases.
• High blood pressure and the metabolic syndrome.
• Diabetes mellitus type II.
• Allergies, asthma, autoimmune diseases and food intolerances.
• Migraine.
• Depression.
• Cancer in certain stages — adjuvant, never as the sole treatment.

This classification is always attributed to the ÄGHE and the medical team, never a promise of cure. How well longer fasting under supervision is tolerated is underpinned by the PLOS One study: among the 1,422 accompanied people, physical and emotional well-being rose markedly in all groups, and of the participants with existing health complaints a large share reported an improvement. Whether therapeutic fasting fits in an individual case nevertheless always belongs, at the Tannerhof, to medical clarification — because every person is different, and the individual stands at the centre.

How the Tannerhof accompanies this effect

The two levels of effect do not unfold in a vacuum. At Naturhotel Tannerhof therapeutic fasting is always medically supervised, because the house's medical experience belongs together with the fasting process. The doctors at the Tannerhof are experts in fasting; they accompany values and circulation as well as the individual course. The start is the medical intake consultation on the first fasting day, holistically designed with anamnesis, physical examination including bioimpedance analysis to measure body composition, and a medication review. The length of stay is booked before arrival; from the intake consultation onward the course can be coordinated together and extended if needed.

The accompanying range of therapies is deliberately broad. The medical applications include bioimpedance analysis, IHHT altitude training depending on the programme and, where medically appropriate, ozone autohaemotherapy. Added to this are compresses and wraps such as the liver-supporting hayflower wrap, aroma wraps as well as mud and warm packs, baths and pours such as the Kneipp alternating pour and magnesium-rich detox baths, massages such as the fasting massage, the detox massage with Königsöl or the acidosis massage, lymphatic drainage and foot reflexology, plus breathing therapy and sauna sessions. Movement remains part of fasting, dosed moderately: moderate base endurance training and moderate strength training, yoga, Feldenkrais and Tai Chi. Summit tours and running are possible, only at a pace that suits fasting — the body nourishes itself from within.

Over all of this lies the place. Bayrischzell, the alpine meadow, the mountain stream, clear and pure mountain air and the view to the Wendelstein. Surroundings and medical supervision work as equals here: fasting in a moving landscape becomes more intense, and the supervision gives the process direction. My hideaway in the mountains is the calm setting in which both levels of effect are given room.

So the effect stays in everyday life

Fat burning ends with refeeding, autophagy is a recurring process — both can be made lasting. In the closing consultation with the accompanying doctors, what has changed is evaluated and how nutrition can look afterward is discussed. If a lasting change is wanted, the Schlanke Tanne Low Carb can follow, the house's own low-carb diet. Intermittent fasting too, for instance in a 16/8 rhythm, is a recommended way to carry the benefits of compact fasting into everyday life — not a Buchinger substitute, but its extension into the ordinary day. Anyone wanting to think of the fasting axis beyond the single stay will find the right framework in the Longevity at the Tannerhof programme.

This turns the effect of a fasting week into more than a brief effect. It gains a continuation — and perhaps that is exactly the old Tannerhof phrase in present-day form: Become essential.