Can eating "cold rice" help you lose weight? What you need to know about resistant starch

I heard that cooling down cooked rice, steamed buns, bread and other staple foods will produce resistant starch, which will reduce the calories of the food. Eating such staple foods can help you lose weight! How many of you have tried this "cold rice weight loss method"?

Can you still eat such fragrant hot rice? | Tuchong Creative

Is this weight loss method reliable? Is there any scientific basis for it?

Let me first state the conclusion. In principle, cooling down staple foods to produce resistant starch has a positive effect on weight loss, but the effect is limited and it should not be used as the main method of weight loss.

Let’s talk about it in detail below.

01

What is Resistant Starch?

Starch is a carbohydrate formed by the polymerization of glucose molecules. It is one of the important forms of energy storage in plants and an important source of carbohydrate nutrients for humans.

Starch is a relatively large family. According to the difficulty of digestion, it can be divided into three categories: [1]

Fast-digesting starch: can be digested and absorbed in the small intestine within 20 minutes, such as baked potatoes, ripe bananas, etc.

Slowly digestible starch: can be digested and absorbed in the small intestine within 20 to 120 minutes, such as natural corn starch.

Resistant starch: It cannot be digested and absorbed in the small intestine and is found in seeds, grains, and some staple foods that have been cooled. For example, cold rice increases its resistant starch content after it has been cooled.

The starch we usually use for cooking | Tuchong Creative

Resistant starch is also a kind of dietary fiber. Although it cannot be absorbed and utilized in the small intestine, it can reach the colon after 2 hours and be fermented by the microbial flora in the colon. It helps to increase the level of short-chain fatty acids, lower intestinal pH, reduce the number of pathogens in the intestine and increase the number of probiotics, which is beneficial for preventing colon diseases.

In addition, resistant starch has the benefits of lowering blood cholesterol, reducing the risk of obesity, and helping to control blood sugar.

02

Cold rice helps lose weight because of resistant starch

Under normal circumstances, the starch structure contained in rice is amylose. During the process of steaming and cooking rice, amylose will absorb water, swell and gelatinize. At this time, the starch in the rice is fast-digesting starch, and amylase can freely break them down into glucose for use by the human body.

However, if the cooked rice is not eaten but is refrigerated, it will "age and regenerate" at low temperatures. At this time, the content of resistant starch in the rice, that is, the part of starch that is not digested by the small intestine, increases, and it cannot be broken down into glucose for use.

Experiments have shown that after ordinary glutinous rice is placed in the refrigerator for 24 hours, the resistant starch content increases from 4% to 14%, an increase of 10%. [2]

Since the caloric value of resistant starch is only about half of that of fast-digesting starch, an increase in the content of resistant starch will lead to a decrease in the calories that can be absorbed from the rice eaten, which will help with weight loss to a certain extent.

03

Some staple foods are useless if they are cooled!

Since putting rice in the refrigerator may help you lose weight, does that mean all staple foods have the same effect when eaten cold?

Not at all!

Whether the resistant starch content of staple foods increases after cooling has a lot to do with the composition of the food starch. The effect will be greater for foods with high amylose content, while this effect will be smaller for foods with high amylopectin content.

Because long-term refrigeration at low temperatures will make the molecules of amylose tend to be re-ordered, forming crystalline areas, showing a regeneration effect, and becoming resistant to amylase. However, for foods with high levels of amylopectin, such as glutinous rice, refrigeration has little effect on their digestion speed and blood sugar response, and may even make the blood sugar response stronger. [2, 3]

Schematic diagram of the difference between amylose (left) and amylopectin (right) | TuChong Creative

Therefore, for rice, steamed buns, and bread with high content of amylose, the content of resistant starch will increase significantly after refrigeration; but for glutinous rice foods with high content of amylopectin, such as rice balls, Yuanxiao, and rice dumplings, don't count on it. Even if they are cooled, they will not help with weight loss and blood sugar control.

04

These factors also affect resistant starch

In addition to the structure of starch affecting the production of resistant starch, the following four factors are also involved: [4]

① The longer the rice is heated, the more it promotes the resistant starch content produced by its aging and regeneration.

② Slow cooling is more conducive to the production of resistant starch than rapid cooling. Because the linear molecules in the starch gel do not have time to recrystallize and aggregate during rapid cooling, it is not easy to form resistant starch. Therefore, do not freeze it, but refrigerate it.

③The most suitable refrigeration temperature is 0~4℃, at which the crystals grow faster, which is conducive to aging and regeneration. In addition, the entire process of resistant starch production is generally completed within 24 hours.

④ Food with too high water content is not conducive to aging and rejuvenation. Usually, food with a water content of more than 60% is not conducive to the production of resistant starch, such as porridge.

Some people may have such a question: What if it is cooled and then heated again? Will the resistant starch still be there?

Unfortunately, if cold rice is reheated, the resistant starch content will decrease, and it will be much lower. In the end, the resistant starch content will be even lower than when the rice is just out of the pot. Naturally, you can forget about the weight loss effect by eating this reheated rice.

Summarize:

Although in principle, eating cold rice is helpful for weight loss, weight loss depends on the overall calorie intake level. Even if you eat cold rice every day, the total calorie intake is still high and it is still difficult to lose weight. Therefore, eating cold rice does not play a decisive role in weight loss.

In addition, long-term consumption of cold rice and cold steamed bread may cause gastrointestinal discomfort, so this weight loss method needs to be chosen with caution. If you have the willpower to eat cold rice, it is better to eat a reasonable diet and increase exercise, and the weight loss effect will be better!

Author | Xue Qingxin, member of Chinese Nutrition Society, registered dietitian, health manager, public nutritionist

Reviewer | Song Shuang, Associate Researcher, Institute of Nutrition and Health, Chinese Center for Disease Control and Prevention

Editor | Ding Zong

References:

[1] Zhu Ping, Kong Xiangli, Bao Jinsong, et al. Research progress on the application and efficacy of resistant starch in food[J]. Journal of Nuclear Agricultural Sciences, 2015, 29(2): 327-336. DOI: 10.11869/j.issn.100-8551.2015.02.0327.

[2] Wang Lu, Fan Zhihong, Shi Haiyan, et al. Starch digestibility of several glutinous foods[J]. Food Science, 2010, 31(17): 359-363.

[3] Wang Shuying, Fan Zhihong, Zeng Yue, Liu Fang, Liu Bo. Effects of different rice on postprandial blood glucose and satiety response[J]. Acta Nutrimenta Sinica, 2013, 35(03): 236-240. DOI: 10.13325/j.cnki.acta.nutr.sin.2013.03.014.

[4] Yu Shifeng, Zheng Xiqun. Research progress on the influencing factors and formation mechanism of RS3 resistant starch in rice[J]. Food Industry Science and Technology, 2012, 33(8): 431-435.

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