Fruits and Nuts as a Post-Fast Diet: Pros, Cons and When It Works

After a fast — whether it's 16 hours or several days — what you eat next matters enormously. Break the fast wrong and you undo much of the benefit. Break it right and you ride the wave of the clean metabolic state fasting creates. Upton Sinclair, in his 1911 book The Fasting Cure, was fascinated by what he called the "raw food" approach after fasting: a diet built primarily on fruits and nuts. It worked brilliantly for some. For others, not so much.

What Upton Sinclair Observed in 1911

Sinclair was writing at a time when raw food enthusiasts were gaining influence in health circles. After his own 12-day fasts, he experimented extensively with what to eat afterward. He tried milk diets (which worked exceptionally well for him initially), milk plus broiled lean beef (which he found supported his intensive intellectual work), and the fruit-and-nut approach that many of his correspondents recommended.

His conclusion, framed honestly: fruits and nuts worked well for people who were physically active — but failed him when he was doing sustained mental work. He wrote that this diet left him "unable to produce sustained intellectual output" and that he ultimately found broiled lean beef the only food that let him "write incessantly."

That said, his 277-case survey included many people who thrived on a fruit-and-nut approach in the weeks following extended fasts. The results weren't universal — they were deeply individual.

The Logic Behind This Approach

The case for fruits and nuts as a post-fast reintroduction diet is intuitive:

Easy digestion. After an extended fast, the digestive system has been resting. Stomach acid production decreases, digestive enzymes downregulate, and the muscular contractions of peristalsis slow. Raw fruits are mostly water and simple sugars — they pass through quickly and require minimal digestive effort. Nuts, rich in fat and protein, digest slowly and provide sustained energy.

Minimal fermentation risk. Sinclair's core theory of disease was that carbohydrates — especially starch and refined sugar — ferment in the gut and create toxins. Fruits, particularly tropical fruits, and raw nuts don't go through the same putrefaction process as starches like bread and rice. From his perspective, this made them safer re-entry foods.

Natural nutrient density. Fruits provide quick glucose for the re-awakening digestive system, along with vitamins, minerals, and fibre. Nuts offer fat, protein, and minerals including magnesium and zinc. Together, they create a reasonably balanced restart.

The Sinclair Reference: The Fasting Cure (1911)

In his book, Sinclair documented his dietary evolution with characteristic candour. He writes: "I recommend a fast, and then a diet of fruits and nuts and other raw foods. But I have to admit that for myself, I found this insufficient for sustained intellectual labour. I ultimately found that broiled lean beef enabled me to work as nothing else did."

This honesty is rare in health writing of any era. Sinclair acknowledged that what worked for physical labourers and people living active outdoor lives did not necessarily work for people producing large volumes of written work.

He drew on the ideas of the Victorian dietary reformer Dr. Salisbury, who argued that starch and sugar create an intestinal "yeast-pot" — exactly what you want to avoid reintroducing after a fast has cleared out the system.

Sinclair, U. (1911). The Fasting Cure. Mitchell Kennerley.

The Modern Science View

A century of nutritional research allows us to layer modern context onto Sinclair's observations:

Fruits re-enter the picture carefully. Fructose — the main sugar in fruit — is processed exclusively by the liver. After an extended fast, the liver's glycogen stores are depleted, which makes it very efficient at absorbing fructose initially. However, large amounts of fructose consumed rapidly can overwhelm liver capacity and contribute to fat accumulation. Post-fast is not the moment to eat large bowls of high-fructose fruit.

Low-fructose fruits — berries, kiwi, citrus — are a better post-fast choice than high-fructose options like mangoes, grapes, or dried fruit.

Nuts provide a slow fuel source. Raw, unsalted walnuts, almonds, and pecans are excellent post-fast foods: dense in fat and protein, with no significant impact on blood sugar. They keep insulin low while providing calories for the recovering body.

The protein gap. One limitation of a pure fruit-and-nut diet is relatively modest protein intake compared to what muscles need after a fast — especially if the person has been active. Modern sports nutrition research suggests consuming 25–40 grams of complete protein in the first meal after an extended fast helps preserve muscle and support recovery. This is hard to achieve from fruits and nuts alone without very large quantities of nuts.

When This Approach Works Well

The fruit-and-nut approach works best in these situations:

• Following a 1–3 day fast, when easing back in with light, easy-to-digest foods reduces the risk of digestive distress
• For people in sedentary roles where protein demand is lower
• In warm climates where fruit is seasonal and fresh — the nutrient profile is different from commercially grown, out-of-season produce
• As a transitional phase — 1–2 days of fruits and nuts, then moving to more substantial meals with meat, eggs, or fish

When This Approach Falls Short

As Sinclair himself observed, a pure fruit-and-nut diet after fasting is insufficient for:

• People doing sustained mental or physical work who need dense protein and fat for neurotransmitter synthesis and energy
• Those with blood sugar instability — high fruit intake, especially tropical fruits, can spike insulin and restart the blood sugar rollercoaster
• Anyone with low muscle mass or trying to build muscle alongside fasting

What the Book Intermittent Fasting in Practice Recommends Instead

The modern fasting approach in Intermittent Fasting in Practice is more straightforward. After any fasting window, break with:

• Start with something light: a salad, leafy greens, fermented vegetables like kimchi or sauerkraut
• Move to your main meal: quality protein (meat, fish, eggs), healthy fats (butter, olive oil, avocado), and non-starchy vegetables
• Eat slowly — the digestive system has been resting and shouldn't be hit hard

Fruit is not the first priority in modern fasting approaches because most people are fasting daily (16–20 hours), not doing extended multi-day fasts. The goal is stable blood sugar, not digestive ease from light foods. Berries in small amounts are fine; large fruit portions are not recommended until goal weight is achieved.

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Frequently Asked Questions

Can you eat fruit after intermittent fasting?

In small amounts, yes — especially low-fructose fruits like berries, kiwi, and citrus. Large amounts of high-fructose fruit (mango, grapes, dried fruit) are best avoided, particularly if you're trying to lose weight, as they can spike insulin and disrupt the fat-burning state fasting created.

Are nuts good to eat after a fast?

Yes. Raw, unsalted nuts — walnuts, pecans, almonds — are an excellent choice after a fast. They provide fat, protein, and minerals without spiking blood sugar. Avoid flavoured or roasted nuts with seed oils or sugar coatings.

What did Upton Sinclair eat after his fasts?

Sinclair tried several approaches: the milk diet (which gave extraordinary early results), then fruits and nuts (which worked for physical energy but not for sustained writing), and ultimately broiled lean beef with hot water, which he described as the only food that supported his intensive intellectual work long-term.

How long should you wait before eating fruit after an extended fast?

After a fast of 3 days or more, it's best to start with small amounts of fruit juice (orange juice or grape juice diluted with water) for the first 1–2 days, then move to small amounts of whole fruit before introducing more substantial foods. The digestive system needs gradual reintroduction.

What is the best first food to eat after breaking a fast?

For a daily 16–20 hour fast: a salad or fermented vegetables, then a protein-rich main meal. For an extended multi-day fast: small amounts of orange juice or clear broth first, then light foods like fruit, then building up over 2–4 days to full meals.

Related Articles

• How to break a fast safely: a step-by-step guide
• Why you must reintroduce food slowly after fasting
• The best diet after a fast: what research and historical cases agree on

This article draws on historical research from 1911 and is for informational purposes only — not medical advice. Always consult a qualified healthcare professional before making any dietary changes.