Are leftover pasta, rice and potatoes really healthier?
Pasta, rice and potatoes have one thing in common: they’re full of starch. Heated and cooled down again, it turns into resistant starch, which is supposed to aid weight loss and be healthier. But is there any validity to this health hack?
The internet, and social media in particular, loves to hype up supposed health hacks that turn out to be complete nonsense on closer inspection. The idea that classic carb bombs like pasta, rice and potatoes could suddenly become a weight-loss aid and health boost with one simple trick sounds like yet another myth.
The claim? If you leave cooked pasta, rice and potatoes to sit until the next day, some of the starch turns into what’s called resistant starch, which the body can only absorb to a limited extent. Supposedly, this means you can eat them without putting on weight, and even do your gut bacteria a favour while you’re at it. A kind of leftovers-turned-superfood.
Sounds too good to be true, doesn’t it? (Not to mention that fresh pasta frankly tastes way better – though that’s just my opinion.) And that’s reason enough to take a closer look at the science behind this «nutritional miracle».
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How cooked starch becomes resistant starch
Starch is essentially just a bunch of sugar molecules chained together that plants use as an energy store. In freshly cooked pasta, rice or potatoes, it’s mostly present in a form our digestive enzymes can break down very easily. The molecule chains are loosely coiled, the starch swells and is therefore easy to break down.
The crux: once it cools down again after cooking, the structure of the starch changes; some of the starch chains pack together more tightly, forming small, dense regions that are harder for the digestive enzymes to access. This is how a specific type of resistant starch – retrograded starch, or RS3 for short – forms. Resistant starch is starch that passes through the small intestine undigested and is only broken down by bacteria in the large intestine.
Bacteria in the large intestine ferment this resistant starch, producing short-chain fatty acids – mainly acetate, propionate and butyrate. Butyrate is an important energy source for the gut lining and is associated with more favourable and anti-inflammatory conditions in the gut.
What this means for calories, blood sugar and your gut
At first glance, that sounds promising. But what exactly does it mean for calorie content and blood sugar? This is where the picture becomes more sobering: although resistant starch does provide slightly less energy than fully digestible starch, the difference is small. In a typical portion of leftover pasta, rice or potatoes, it only amounts to a few kilocalories – not enough to lose a significant amount of weight from that alone. It’s a different story when it comes to blood sugar. Several studies show that meals with a higher proportion of resistant starch slightly reduce the rise in blood sugar after eating. Further systematic reviews found that a higher intake of resistant starch leads to somewhat better fasting blood sugar and insulin levels in people with prediabetes or type 2 diabetes, and in some cases to slightly improved long-term blood sugar levels. But more pronounced effects generally only occur at much higher intakes of resistant starch than what's in a few grammes of leftover pasta.
Source: Olegarx/Pexels
And there’s a catch. How much resistant starch forms during cooling, and how stable it remains on reheating, depends on the food and how it’s prepared. Studies suggest that cooling rice, potatoes and pasta can increase the proportion of resistant starch compared with their freshly cooked counterparts. Some of this effect is retained on reheating, especially in rice and fresh pasta, while it partly diminishes again in potatoes. The reheating method also matters; microwaves seem to preserve resistant starch better than prolonged simmering on the hob.
Lower blood sugar spikes, yes – a trick for weight loss, no
At least there’s a grain of truth to the hype around leftover pasta and the like, which is more than can be said for many other health miracles you read about online. The truth in a nutshell: more RS3 (retrograded starch) instead of «normal» starch can slightly reduce the blood sugar spike after eating. It also feeds beneficial bacteria in the large intestine that can produce anti-inflammatory fatty acids. The nonsense in a nutshell: the idea that carb bombs will help you lose weight if you just leave them lying around long enough.
Science editor and biologist. I love animals and am fascinated by plants, their abilities and everything you can do with them. That's why my favourite place is always the outdoors - somewhere in nature, preferably in my wild garden.
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