What Grandmas Ate to Stay Regular | China, Britain & Japan Compared by Science

When things just won't get moving, what did grandmothers around the world bring out of the kitchen? Today we put three side by side: a sweet potato and ginger soup from Guangdong, China; prunes soaked in tea from Britain and France; and Japan's roasted sweet potato. Then we look at what science has actually checked.

1. Sweet Potato & Ginger Tong Sui (番薯糖水) — Guangdong, China

Where it comes from

Tong sui is a Cantonese sweet soup dessert. In Guangdong, families have long eaten it on chilly days to warm up.

Ingredients (serves 2)

Ingredient	Amount
Sweet potato	200 g (about 7 oz)
Fresh ginger, thinly sliced	10 g (about a 1-inch piece)
Brown sugar	20 g (about 2 Tbsp)
Water	600 ml (about 2½ cups)

How to make it

1. Cut the sweet potato into bite-size pieces.
2. Simmer with the water and ginger for 20 minutes.
3. Add the brown sugar and simmer 5 minutes more.

What science says

Sweet potatoes contain fiber, but no study has looked at sweet potato soup and constipation. In human studies, ginger has mainly been shown to ease nausea. Sipping it warm is also a nice way to get some fluids.

Rating: Evidence ★ · Safety 🟢 · Best enjoyed: on a chilly day, 1 bowl

Caution: If you limit potassium because of kidney disease, eat less sweet potato or skip it. Sweet potatoes are high in potassium. When kidney function is low, potassium doesn't leave the body easily, blood potassium can rise, and that can affect your heart rhythm.

2. Prunes Soaked in Tea — Britain & France

Where it comes from

In Britain and France, "prunes for constipation" has been common wisdom for a very long time. The British way is to soak them in black tea.

Ingredients (serves 2)

Ingredient	Amount
Prunes (dried plums)	50 g (about 6 prunes)
Hot black tea or water	100 ml (about ⅓ cup + 1 Tbsp)

How to make it

1. Put the prunes in a bowl.
2. Pour the hot tea over them.
3. Once cool, soak overnight in the fridge and eat them with the liquid.

What science says

In a small randomized trial of 40 people with chronic constipation, eating 6 prunes twice a day increased how often they went, and prunes did better than psyllium. Keep in mind the study wasn't blinded and had industry support. Prunes also contain fiber, and the warm liquid adds fluids.

Rating: Evidence ★★ · Safety 🟢 · Best enjoyed: when you feel backed up, starting with about 6 a day

Caution: If you limit potassium because of kidney disease, eat fewer prunes or skip them. Prunes are high in potassium. When kidney function is low, potassium doesn't leave the body easily, blood potassium can rise, and that can affect your heart rhythm. Caution: Start with about 6 a day. Twelve prunes add up to about 260 kcal, which is quite a lot.

3. Roasted Sweet Potato (Yaki-imo, 焼き芋) — Japan

Where it comes from

A winter street favorite in Japan, where people have long said that sweet potatoes keep you regular.

Ingredients (serves 2)

Ingredient	Amount
Sweet potatoes	400 g (about 14 oz; 2 medium)

How to make it

1. Wash the sweet potatoes, wrap them in a damp paper towel, then in foil.
2. Roast at 160°C (about 320°F) for 60–90 minutes (only 5 minutes hands-on).
3. They're done when a chopstick slides right in.

What science says

Sweet potatoes contain fiber, but there isn't enough research on sweet potatoes themselves and constipation. It hasn't been proven — but this simple snack has been loved every winter for generations.

Rating: Evidence ★ · Safety 🟢 · Best enjoyed: in fall and winter, ½ to 1 medium potato

Caution: If you limit potassium because of kidney disease, eat less sweet potato or skip it. Sweet potatoes are high in potassium. When kidney function is low, potassium doesn't leave the body easily, blood potassium can rise, and that can affect your heart rhythm. Caution: If you have diabetes, stick to about half a potato. Roasted sweet potatoes taste very sweet and can raise blood sugar.

The Three, Side by Side

Country	Food	Evidence	Safety
Guangdong, China	Sweet potato & ginger tong sui	★	🟢
Britain & France	Prunes soaked in tea	★★	🟢
Japan	Roasted sweet potato	★	🟢

Prunes have the most research behind them. Sweet potatoes just haven't been tested enough — that's not the same as wrong. Enjoy any of them as food, and if your discomfort keeps going, see a doctor.

General Caution

• If you have diabetes, go easy on sweet ingredients. Sugary foods and drinks can raise blood sugar quickly. (The brown sugar in tong sui.)

Sources

• NCCIH: Ginger
• National Kidney Foundation: Potassium in Your CKD Diet
• AAFP: Prunes vs psyllium for constipation (RCT summary)

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This article introduces traditional food customs. It is not intended to diagnose, treat, cure, or prevent any disease. Please talk to your doctor if you have health concerns.