Mung bean soup, or lu dou tang (绿豆汤), is the drink Chinese families reach for when the heat gets unbearable. It's cheap. It's fast. And for at least a thousand years, it has been the go-to home remedy for clearing what Traditional Chinese Medicine (TCM) calls "summer heat." This guide walks you through the classic recipe, the science behind the bean, and the one detail most people get wrong: the difference between a soup that cools you down and one that doesn't.

Quick Answer

What it does (TCM view): Mung bean (lu dou) is classified as sweet and cold, entering the Heart and Stomach channels. Traditional sources use it to clear summer heat, relieve thirst and restlessness, and "resolve toxicity." This is traditional use, not a clinical claim.
How to make the cooling version: Boil rinsed mung beans hard for about 10-12 minutes with the lid cracked, until the skins just split and the broth turns jade green. Drink the green broth. Don't simmer it to mush if your goal is to clear heat.
What's actually in it: Per 100 g cooked, mung beans give about 105 calories, 7 g protein, 7.6 g fiber, and 159 mcg folate (USDA). The seed coat is rich in the flavonoids vitexin and isovitexin, which lab studies link to antioxidant and glucose-related activity.
Who should be careful: People with a cold, weak digestion (TCM "Spleen yang deficiency") — chronic loose stools, cold hands and feet, bloating after cold food — should limit it or eat it cooked into warm congee with ginger. It's a cold food.

Medical disclaimer: This article is educational and describes traditional food practices plus published nutrition research. It is not medical advice and does not diagnose or treat any condition. Mung bean soup is a food, not a drug. If you're pregnant, managing diabetes or kidney disease, taking medication, or have ongoing symptoms, talk to a licensed clinician before using food therapeutically.

What Is Mung Bean Soup (Lu Dou Tang)?

Lu dou tang is one of the most familiar food-medicines in Chinese culture. At its simplest, it's nothing but small green mung beans (Vigna radiata) boiled in water. No meat. No oil. Sometimes a little rock sugar, sometimes nothing at all.

In summer, street vendors and home kitchens across China, Taiwan, and the wider diaspora make it by the pot. People drink the cool broth straight, eat the soft beans with a spoon, or chill the whole thing and pour it over ice. In TCM food therapy — known as yao shan, or medicinal cuisine — it's the textbook example of a "cooling" dish for a hot season.

Here's the thing most recipes skip. There are really two soups hiding inside one pot.

The clear green broth (skins just cracked, short cook) is the one used to clear heat. The cooling power lives in that thin, jade-colored liquid.
The thick, mushy porridge (long simmer, beans broken down) is more nourishing and filling, but the classic teaching is that boiling it to death dulls its heat-clearing edge.

If summer cooling is your goal, you want the green broth. We'll cover how to get it below.

Where the tradition comes from

Mung bean shows up as a medicinal food early in the Chinese record. It was noted as a food and folk remedy well before it was formally listed, and by the Tang dynasty the physician Sun Simiao had recorded its use for heat-type conditions. The big endorsement came in the Ming dynasty: Li Shizhen's Bencao Gangmu (Compendium of Materia Medica, 1578) praised mung bean's detoxifying power, calling it cold in nature and useful to "clear heat and resolve toxin." (See the Lu Dou herb monograph at Me & Qi for a translated summary of these classical attributions.)

These are traditional descriptions. They explain how the food was used and categorized, not a modern clinical trial. Keep that distinction in mind throughout — it matters for honesty and for safety.

Why Is Mung Bean Considered "Cooling" in TCM?

In Chinese medicine, every food has a nature (temperature) and a flavor. These aren't about how hot the dish is on the stove. They describe the effect the food is thought to have on the body after you eat it. You can read the full framework in our explainer on what "cooling foods" mean in TCM.

Mung bean lands firmly on the cold end.

Mung bean (lu dou) at a glance — TCM properties

TCM property	Classification	What it traditionally means
Nature (temperature)	Cold (寒)	Used to cool internal heat; can over-cool a cold body
Flavor	Sweet (甘)	Mildly nourishing, harmonizing; easy on the system
Channels entered	Heart, Stomach	Targets heat showing up as restlessness, thirst, mouth sores
Traditional actions	Clear summer heat, relieve thirst, resolve toxicity, promote urination	Hot-weather drink; folk antidote use
Best season	Summer (and late spring heat)	Peak use during "summer heat" (shu) patterns

"Summer heat" (暑, shu) is a specific idea in TCM. The Huangdi Neijing (Yellow Emperor's Inner Classic), the foundational text of Chinese medicine, frames health as keeping yin and yang in balance with the seasons. Summer is the most yang season — hot, expansive, draining. When that external heat overwhelms you, the classic signs are thirst, sweating, irritability, dark scanty urine, flushed face, and that wiped-out, heavy feeling on a sticky afternoon.

A cold-natured, fluid-rich food like mung bean soup is the traditional counterweight. It's the same logic behind a whole family of summer cooling recipes in Chinese tradition — eat cold-natured foods to offset a hot-natured season.

What Are the Nutrition Facts and Benefits of Mung Bean Soup?

Strip away the tradition and you still have a genuinely good food. Mung beans are a legume, and they bring the legume résumé: plant protein, fiber, folate, and minerals, with very little fat.

Cooked mung beans — nutrition per 100 g

Nutrient	Amount (per 100 g cooked)	Why it matters
Calories	~105 kcal	Light; easy to drink a big bowl
Protein	~7 g	Solid plant protein for a bean
Carbohydrate	~19 g	Mostly slow-digesting starch
Dietary fiber	~7.6 g	Roughly a quarter of daily needs
Fat	~0.4 g	Naturally near fat-free
Folate	~159 mcg (~40% DV)	Important in pregnancy and red blood cell formation
Magnesium	~48 mg	Muscle and nerve function
Potassium	~266 mg	Fluid and blood pressure balance
Iron	~1.4 mg	Plant (non-heme) iron

Values from USDA FoodData Central for mung beans, mature seeds, cooked, boiled. Check the live database at fdc.nal.usda.gov for the current entry.

Note that soup made from a small handful of beans in a lot of water is more dilute than the per-100 g figures suggest. You're drinking it mostly for hydration, electrolytes, and the dissolved plant compounds — not as a protein shake.

What the research actually shows

The interesting science sits in the bean's green seed coat, which is loaded with two flavonoids: vitexin and isovitexin. More than 90% of these compounds live in that coat — another reason the classic "drink the green broth" method makes sense, since the cooking water pulls color and compounds out of the skins.

A 2019 review in Nutrients concluded that mung bean is a good source of protein, fiber, and bioactive polyphenols, and summarized animal and lab evidence that mung bean or its compounds may help with blood glucose, blood lipids, and inflammation (Hou et al., 2019, PMID 31159173). This is a review of mostly preclinical work, not proof of benefit in people.
Vitexin and isovitexin are described as the major antioxidant components of mung bean, and a 2011 PLoS One study found these flavonoids had antioxidant activity and helped protect cells under heat stress in lab models (Cao et al., 2011, PMID 21695166). Worth noting: that "heat stress" is cellular stress in a dish, not a person standing in the sun — but it's a charming overlap with the tradition.
A 2016 study in the Journal of Agricultural and Food Chemistry characterized mung bean phytochemicals and reported antioxidant and tissue-protective (myocardial) activity in a lab/animal model (Bai et al., 2016, PMID 27184346).
A 2024 human study in Nutrients gave purified vitexin and iso-vitexin from mung bean seed coat to overweight adults and reported changes in post-meal glucose response and gut microbiota (Yutharaksanukul et al., 2024, PMC11396884). This used concentrated isolated compounds, not a bowl of home soup — so don't read it as "soup lowers blood sugar."
A 2025 metabolomics paper in Food Production, Processing and Nutrition identified vitexin, isovitexin, and catechin as hypoglycemic factors in mung bean using lab assays (Springer, 2025, DOI 10.1186/s43014-025-00318-z).

The honest bottom line: The flavonoid story is real and promising, but most of it is test-tube and animal work, plus a small human trial on concentrated extracts. None of it proves that a bowl of mung bean soup treats disease. Enjoy the soup for what it is — a hydrating, low-fat, nutrient-decent traditional cooler.

How Do You Make Traditional Mung Bean Soup (Step by Step)?

This is the classic clear, cooling version — the one for hot days. It's almost embarrassingly simple, which is the whole point.

Ingredients

Ingredient	Amount	Notes
Dried green mung beans	1 cup (about 200 g)	Whole, with skins on — the skins do the cooling work
Water	5-6 cups	More water = thinner, more "broth-forward" cooling soup
Rock sugar	1-2 tbsp, to taste (optional)	Add at the end; or leave it out entirely
Salt	tiny pinch (optional)	Some families add a pinch to deepen flavor

That's it for the base. Optional cooling add-ins below.

Method

Rinse and quick-soak. Rinse the beans until the water runs clear. Pick out any shriveled or floating beans. Soak for 30 minutes to 2 hours if you have time. Soaking isn't strictly required, but it speeds cooking and helps the skins crack evenly.
Boil hard, lid cracked. Add beans and cold water to a pot. Bring to a rolling boil, then keep it at a strong simmer with the lid slightly open. A vented lid lets steam escape and helps keep the broth bright green instead of cloudy and dark.
Watch for the crack — this is the key step. After about 10-12 minutes of hard boiling, the skins will just begin to split and the water turns a clear jade green. For the cooling soup, stop here. Ladle out the green broth.
Drink the green liquid for cooling. This thin, green-tinged broth is the part TCM associates with clearing heat. Drink it warm, room temperature, or chilled.
(Optional) Keep cooking for a hearty version. Want a filling porridge-like bowl instead? Keep simmering another 20-30 minutes until the beans burst and turn soft and mushy. Add rock sugar at the end. This version is more nourishing and food-like — but the classic teaching says the long boil trades away some of the sharp heat-clearing quality.
Sweeten and serve. Stir in rock sugar only after cooking, off the heat. Chill in the fridge for a refreshing summer drink, or serve warm.

Pro tip on color: Cooking in alkaline (hard) water or over-boiling turns the soup reddish-brown. A tiny squeeze of lemon keeps it greener by slowing chlorophyll breakdown. Green broth isn't just prettier — in the tradition, the fresh green liquid is the most "cooling."

Two soups, one pot — pick your goal

Goal	Cook time	Texture	Traditional use
Clear summer heat	~10-12 min, skins just cracked	Thin green broth	Cooling drink for hot days, thirst, restlessness
Nourish and fill	~35-45 min total	Thick, beans burst, mushy	Light meal, gentler everyday food

Cooling add-ins (TCM-friendly)

Kelp or kombu (海带): Adds minerals and, in tradition, supports softening and downward-clearing.
Fresh mint: A few leaves at the end brighten flavor and add a cooling, surface-releasing quality.
Lotus seeds or dried lily bulb: Push the soup toward calming and yin-nourishing. For a sweet dessert spin, see our mung bean and lotus seed dessert soup.
A piece of dried tangerine peel (chen pi): A classic trick to offset the cold and protect digestion — it warms and moves, balancing the bean's chill.

Who Should Avoid Mung Bean Soup?

This is the part skipped by most "detox soup" blog posts, and it's the most important section for safety. Mung bean is cold. Cold food is great for a hot, excess-heat situation — and a problem for a cold, weak one.

Be cautious or limit it if you have:

A cold, weak digestion (TCM "Spleen yang deficiency"). Telltale signs: chronic loose stools or diarrhea, bloating after eating, feeling worse from cold or raw foods, cold hands and feet, low appetite, fatigue. Piling cold mung bean soup on top of this can worsen the cold and the loose stools. This overlaps with what we describe in the yang-deficiency warming-foods guide.
Generally cold-natured constitution. If you run cold, get chilled easily, and tend toward sluggish digestion, daily iced mung bean soup may not suit you. Eat it warm, in small amounts, and cooked with ginger or chen pi to take the edge off.
Recovering from cold or chills. During a cold-type illness (chills, no thirst, clear runny nose), cooling foods aren't the move. Cooling foods are for heat patterns.

Practical ways to soften the cold nature

You don't have to give it up entirely. The tradition offers fixes:

Cook it as a warm congee with rice rather than a chilled drink.
Add a slice or two of fresh ginger, or a piece of dried tangerine peel (chen pi), while cooking.
Eat it warm, not iced, and keep portions modest.
A little brown sugar also nudges it toward neutral.

Everyone else: simple cautions

G6PD deficiency note: The serious bean to avoid in G6PD deficiency is the fava bean (broad bean), which can trigger favism. Mung bean is a different bean and is not the classic favism trigger. Still, if you have G6PD deficiency, run any new bean-heavy habit past your doctor.
Diabetes or blood-sugar meds: Mung bean soup is generally low-glycemic and bean-based, but the extract studies above used concentrated compounds. Don't treat the soup as a substitute for your medication, and monitor as usual.
Herb timing: Folk tradition holds that mung bean can "neutralize" some substances. If you take Chinese herbal formulas or medications, it's reasonable to separate a big bowl of mung bean soup from your doses by an hour or two, and check with your herbalist or pharmacist.

If you're not sure which camp you're in, our self-assessment of TCM body type is a useful starting point, and the damp-heat constitution food guide covers exactly the pattern mung bean suits best.

How Often and How Much Should You Drink It?

There's no medical dosing here — it's food. But the tradition and common sense point to moderation.

Situation	Reasonable approach
Hot summer day, you run warm	1 bowl (about 1-2 cups broth) per day, warm or chilled
Heat signs (thirst, irritability, mouth sores)	A few bowls over a week during the heat wave
Cold/weak digestion	Small amounts, warm, with ginger/chen pi; skip the iced version
Out of summer / cold weather	Occasional and warm; it's a hot-season food by design

The classic guidance treats lu dou tang as a seasonal drink. It shines in summer heat and during the late-spring warm-up. Drinking ice-cold mung bean soup every day through winter isn't aligned with the tradition's logic. For the bigger picture on matching food to season, see our seasonal eating framework in TCM.

A note on the word "detox." In TCM, mung bean is said to "resolve toxicity" — a traditional concept tied to clearing heat and helping the body process certain poisons, historically even cited against aconite and arsenic poisoning in classical texts. That is not the modern wellness sense of "flushing toxins from your system." Your liver and kidneys do that. Mung bean soup is a hydrating, fiber-containing food that may support normal function — full stop. Be skeptical of any product promising a dramatic cleanse. We unpack this more in our look at TCM "detox" soups and what they really do.

Frequently Asked Questions

1. Should I eat the beans or just drink the broth? For clearing summer heat, the tradition emphasizes the clear green broth — that's where the cooling flavonoids from the skins end up. You can absolutely eat the soft beans too for the protein and fiber; just know the cooling action is strongest in the fresh green liquid from a short boil.

2. Why did my mung bean soup turn red or brown instead of green? Usually it's over-boiling or alkaline (hard) water. The green color comes from compounds in the skins that oxidize and darken with long cooking or high pH. Boil with the lid cracked, don't over-simmer, and add a small squeeze of lemon to help hold the green. The brown soup is still fine to drink — it's just considered less "cooling."

3. Can I drink mung bean soup every day? In hot weather, a daily bowl is fine for most people who run warm. But it's a cold-natured food, so if you have weak, cold digestion or it's not summer, scale back, drink it warm, and cook it with ginger or dried tangerine peel. Listen to your body — if cold drinks give you loose stools or bloating, that's your signal.

4. Is mung bean soup safe during pregnancy? Mung beans are nutritious and high in folate, which is valuable in pregnancy. The cold nature means warm, well-cooked, modest portions are the sensible approach — chilled, iced versions less so. Because pregnancy is individual, confirm with your prenatal provider, and see our note on TCM pregnancy food traditions, which is educational and not medical advice.

5. Does mung bean soup actually detox you or lower blood sugar? Lab and small extract studies are encouraging on antioxidants and glucose-related activity, but they don't prove a bowl of home soup detoxes you or treats diabetes. Treat it as a healthy, hydrating, low-fat food with a long traditional history — not a medicine. Keep taking any prescribed treatment, and talk to a clinician about your specific situation.

Sources

USDA FoodData Central — Mung beans, mature seeds, cooked: fdc.nal.usda.gov
Hou D, et al. "Mung Bean (Vigna radiata L.): Bioactive Polyphenols, Polysaccharides, Peptides, and Health Benefits." Nutrients, 2019. PMID 31159173
Cao D, et al. "Antioxidant properties of the mung bean flavonoids on alleviating heat stress." PLoS One, 2011. PMID 21695166
Bai Y, et al. "Antioxidant and Myocardial Preservation Activities of Natural Phytochemicals from Mung Bean (Vigna radiata L.) Seeds." J Agric Food Chem, 2016. PMID 27184346
"Effects of Purified Vitexin and Iso-Vitexin from Mung Bean Seed Coat on Antihyperglycemic Activity and Gut Microbiota in Overweight Individuals." Nutrients, 2024. PMC11396884
"Discovery of vitexin, isovitexin and catechin as hypoglycemic factors in mung bean." Food Production, Processing and Nutrition, 2025. DOI 10.1186/s43014-025-00318-z
Lu Dou (Mung bean) TCM herb monograph, with translated classical attributions (Bencao Gangmu): Me & Qi
Classical sources referenced: Huangdi Neijing (Yellow Emperor's Inner Classic); Li Shizhen, Bencao Gangmu (Compendium of Materia Medica, 1578).

Mung Bean Soup (Lu Dou Tang): The Classic Summer-Heat Clearing Recipe