Many people experience a strange “rumbling” feeling in their gut—or what Vietnamese call cồn ruột—after eating glass-noodles (miến). Why does this happen? And more importantly: when is it better to avoid miến altogether to protect your stomach?

What is miến (glass noodles)?

Miến are dried thread-type noodles typically made from starches such as mung bean, cassava, sweet potato, potato or tapioca. They are stored dry and used in soups, stir-fries, salads. Nutritionally:

• They are relatively low in fat, modest in protein and high in carbohydrate (starch).

• Most varieties contain little fibre.
  For example: “Glass noodles … contain about 0.9 g fiber per cup, 39 g carbohydrate per serving” according to one nutritional summary. SpiceSEA Nutrition+1

• Many articles label them as low-glycemic index (GI around 20-45) depending on starch source. Sunright Foods+1

Why might you feel “cồn ruột” (stomach rumbling / intestinal gurgling) after eating miến?

Here are several plausible reasons:

1. Rapid movement of food and gas through the gut
   After a meal, digestion triggers muscle contractions (peristalsis) in the stomach and intestines. Liquids, food, gas are moved and create audible rumbling sounds. Healthline+1
   Miến being a starch-rich food (and sometimes lower in fibre) may move through parts of the gut relatively quickly, or create a mismatch of digestion speed, leading to increased sounds or sensations.

2. Low fibre content and starch composition
   Although miến can have benefit (resistant starch etc), their fibre content is low. Fibre helps slow digestion and stabilise absorption. If you eat a large portion of miến without other foods (vegetables, protein, fibre), digestion may be less buffered—leading to sensations of rumbling or discomfort.

3. Starch fermentation or resistant starch effects
   Some studies show that glass noodles produced from mung bean or other starches have measurable levels of resistant starch (RS) — that is starch not fully digested in the small intestine and reaching the colon where bacteria ferment it. Thai Science+1
   Fermentation can generate gas and contribute to rumbling. Also, individuals with sensitive guts (gas, IBS, gastritis) may perceive this more strongly.

4. Possible over-consumption, or fast eating
   Eating quickly, talking while eating, or ingesting large portions can lead to more swallowed air, more gas production and rumbling. Vinmec International Hospital+1
   Finally, if you have sensitive stomach / gastritis / acid-reflux the mild “cool” nature of miến (in traditional classification) combined with other foods (spicy condiments, sour sauces, heavy oil) may trigger stomach discomfort.

Two key times when you should avoid eating miến (or minimise it) to protect your stomach

Based on the nature of miến and digestion, here are two time-windows when it is advisable to avoid miến:

1. Late evening / after 9 pm
   Eating miến late at night may increase the risk of indigestion and interfere with sleep. Your digestive system slows down during rest hours; a large starch meal may sit longer, ferment and cause discomfort. So if you want miến, it’s better to have it in the morning or around lunch, when your digestive system is more active.

2. Immediately after having heavy fried / oily foods
   If you’ve already eaten a large portion of fried foods (which are “hot” in traditional Vietnamese classification) and then have miến (which is “cool” in that classification) the digestive “balance” may be upset. From a modern view: huge amounts of fat + oil slow digestion; adding a high-starch food immediately on top may over-burden your stomach and intestines — causing rumbling, bloating, discomfort. So avoid stacking miến directly after heavy fried meals; instead wait or choose lighter options.

Practical suggestions for eating miến more comfortably and safely

• Combine miến with vegetables, lean protein (eg chicken, tofu, shrimp) and a moderate amount of oil. This will slow digestion, add fibre and nutrients.

• Eat smaller portions rather than a huge bowl on an empty stomach.

• Chew slowly, eat mindfully to reduce swallowed air and help digestion.

• If you have gastritis, acid-reflux, or sensitive digestion: moderate the amount of spicy/sour condiments when eating miến.

• Avoid eating leftover miến which has been sitting for long hours at room temperature — this may encourage bacterial growth or fermentation-gas generation.

Summary

In short, miến can be a convenient and tasty carbohydrate option. But because of its starch-rich, low-fibre nature and digestion dynamics, it can lead to that “cồn ruột” feeling — especially in sensitive individuals or at certain times (late at night; right after heavy fried food). By selecting the right time, portion size, and meal composition, you can enjoy miến more comfortably and reduce the risk of digestive discomfort.