Five-Day Fasting Mimicking Diet Soup (Vegan, Gluten-Free)

Five days on about 725 calories is easier when there is one thing you actually look forward to. For most people doing a homemade fasting mimicking diet, that thing is soup: warm, filling and almost nothing in calorie terms. This one is made in a single pot, keeps for the whole cycle, and contains no gluten, dairy or nuts. The plan and the research are below the recipe. It is not medical advice, so please read the safety section too.

Method

1. Warm the olive oil in a large pan over a medium heat. Add the onion, carrot and celery with a pinch of salt and cook gently for 10 minutes, until soft but not browned.
2. Stir in the garlic and herbs for a minute, then add the courgette.
3. Pour in the tomatoes and stock. Bring to a simmer and cook for 15 minutes.
4. Add the kale or spinach for the last 3 minutes.
5. Season with salt, pepper and a squeeze of lemon. Leave it chunky, or blend half for a thicker bowl.

It keeps for four days in the fridge, which is exactly one fasting cycle. Make it the day before you start.

Allergens: contains celery. Stock cubes often contain wheat, barley or celery, so check the label if you avoid gluten.

What the fasting mimicking diet is

The fasting mimicking diet (FMD) is five days of eating very little, so the body behaves roughly as if it were fasting while you still get some food. It came out of Valter Longo's lab at the University of Southern California. The boxed version is sold as ProLon by L-Nutra, a company Longo founded and has shares in. The papers disclose that conflict of interest, and you should keep it in mind when reading the headlines.

The published protocol is mostly plants, low in protein and sugar, and fairly high in unsaturated fat:

• Day 1: about 1,100 kcal (roughly 10% protein, 56% fat, 34% carbohydrate).
• Days 2–5: about 725 kcal (roughly 9% protein, 44% fat, 47% carbohydrate).
• Day 6: an easy return to normal food: soups, rice, cooked vegetables.

The low protein is deliberate. Cutting protein is part of how the diet lowers IGF-1, so a DIY version built on chicken breast is a different diet.

A homemade day (days 2 to 5)

Weigh things for the first cycle. A careless handful of nuts can take you well past 725 kcal.

On day 1, have a larger lunch and add a second handful of nuts.

Keeping it gluten-free. The boxed kit includes crackers and soups that not every coeliac will trust. Cooking it yourself is easier to control: check stock cubes, swap crackers for kale crisps or rice cakes, and only use oats certified gluten-free if you tolerate them.

What the studies found

The first human trial, published in Science Translational Medicine in 2017, randomised 100 healthy adults to their normal diet or three monthly FMD cycles. The FMD group lost a little weight and waist, with lower blood pressure, fasting glucose and IGF-1. The biggest changes were in people who started with higher risk factors.

In February 2024, a paper in Nature Communications pooled two trials. It reported lower insulin resistance, less liver fat and a median "biological age" about 2.5 years younger after three cycles, estimated from blood markers. The lifespan claims in some press coverage come from modelling, not from following real people.

In short: small trials, short follow-up, promising markers, and funding ties to the product. Nobody has shown that FMD makes people live longer.

Who should not try it

Skip it, or only do it with your doctor, if you are pregnant or breastfeeding, under 18, underweight, have or had an eating disorder, take insulin or other glucose-lowering drugs or blood-pressure medication, or have kidney or liver disease. Expect to feel cold, tired and short-tempered on days 2 and 3. Stop if you feel faint, and do not drive while light-headed.

If you try it, write down everything you eat over the five days. That record is the most useful thing to bring to a doctor, whatever the result.