Does Eating Fast Make You Fat? (Explained)

Today, it is common knowledge that eating slowly can help you lose weight. However, what happens with fast eaters? Does eating fast make you fat?

photo of me eating fast

“Eating fast does make you fat because rapid eating doesn’t allow enough time for the hypothalamus to release satiety hormones. It usually takes 15-20 minutes to facilitate satiety and eating faster than that can result in overeating or getting hungry soon,” according to the Journal of Epidemiology.

In this article, I will explain everything there is to know about eating fast, and chewing food and compare current research.

What happens when you eat too fast?

When I eat fast, I often feel uncomfortable afterward. My stomach feels like it’s in knots, and I can’t seem to digest my food properly.

It’s not a pleasant feeling, and it usually means that I have to spend the rest of the day feeling bloated and uncomfortable.

Plus, I usually end up either eating more food than normal and still feeling hungry, or continue eating until I’m more than full.

According to a study published in 2006, “when you eat too fast your body doesn’t have time to release a sufficient amount of gastric acid and digestive enzymes, which can lead to digestion problems.”

Here’s the photo that can help you visualize the difference in gastric acid between eating fast and eating slowly.

“Gastric acid is the mix of stomach acids that is part of your digestive system,” states the journal.

“It contains hydrochloric acid, sodium chloride, and potassium chloride. Those acids break down food, split up the proteins, and start to extract nutrients.”

Having enough gastric acid juice during eating is important because “it helps to facilitate nutrient breakdown, digestion, absorption, and further transport.”

“It also helps to protect from microorganisms and bacterial overgrowth,” according to the publication.

In other words, to fully digest, absorb and redistribute essential nutrients you need to have enough gastric juices.

  • Slow eating, smelling, and chewing food for longer facilitate better gastric acid activity.
  • Fast eating and not chewing the food long enough reduces its activity.

Disadvantages of eating fast according to research

Here is the list of disadvantages of eating fast related to health based on current research.

1. Weight gain

In the aforementioned study, Dr. Rei Otsuka from Nagoya University Graduate School of Medicine documented 6651 participants (5179 males and 1472 females) and the effect of eating duration on obesity.

“Participants who reported eating very fast had the highest body weight, compared to participants who reported eating very slowly,” explains Dr. Otsuka.

Here’s the graph that illustrates the correlation between eating tempo and body weight.

photo that describes the effects of eating fast on body weight

2. Higher BMI

“Participants who reported eating slowly also had the lowest BMI. And people who reported eating very fast had the highest,” says Dr. Otsuka.

The same results you can see in the next graph.

photo that describes the effects of eating fast on BMI

Here you can see the correlation between eating duration and BMI in females.

What about males? Is there any difference? Not really.

The next graph shows the difference in BMI in males. As you can see, eating duration had a similar effect on males as on females.

In summary, “eating speed and duration has a massive impact on body weight and BMI among middle-aged men and women,” explains Dr. Otsuka.

Eating fast means chewing fast

According to the article published in Nutrients Journal, “when you don’t chew your food long enough it may delay the onset of satiety by inhibiting oro-sensory signaling.”

“A short duration of chewing reduces feedback to the brain and limits exposure of food pieces to sensory receptors in the mouth,” states the article.

Sensory receptors are important for the food you eat. They help you taste the food and feel the texture. The information from the sensory receptors also helps your stomach release digestive enzymes.

“Chewing is important for digestion because it provides multiple physiological signals and necessary feedback to the brain and the stomach.”

This helps to recognize all information about the food’s nutritional value and provides warning signs for spoiled or poisonous food.

If you do not chew your food long enough, it will not help you feel full and can make you feel hungry again soon.

Disadvantages of fast chewing according to research

Bridget Cassady, Ph.D., is a research scientist and registered dietitian nutritionist from Illinois. In her randomized controlled trial, Dr. Cassady compared a group of people eating 5-g almond portions for s specified number of chews per portion.

  • 10 chews
  • 25 chews
  • 40 chews

(All participants ate almonds.)

The blood samples were collected at various periods of time.

This way, Dr. Cassady explains, “we could easily measure satiety hormone concentration in the blood after each eating session.”

“This is a crucial part of this research because fullness or hunger is very subjective in nature.”

“Each of the participant’s perceptions of fullness or appetite can be inaccurate. However, with the blood samples, there is no need for subjectivity because everything is in the blood,” says Dr. Cassady.

Here’s the graph that illustrates the results on satiety.

photo of satiety difference between eating fast and slow
Cassady, Bridget A et al. “Mastication of almonds: effects of lipid bioaccessibility, appetite, and hormone response.” The American journal of clinical nutrition vol. 89,3 (2009): 794-800. doi:10.3945/ajcn.2008.26669

“Participants who chew the almonds 40 times had the strongest reduction in hunger and increase of fullness,” says Dr. Cassady.

The number of chews was directly related to the satiety effects and to the duration of fullness. Chewing almonds 40 times not only makes people fuller quicker but also this fullness last for longer,” adds Dr. Cassady.

Now watch this.

For me, the most fascinating part of this research was the baseline.

As you can see from the graph above, satiety hormones went below the baseline after chewing almonds 10 times.

This means that chewing your food for a short period of time can actually make you more hungry than before.

Does not chewing food make you fat?

“Not chewing food can inhibit the satiety and fullness response, which often may lead to weight gain,” according to Dr. Cassady.

“Not chewing your food properly also may lead to overeating, without feeling full after. It also down-regulates digestion and limits nutrient extraction,” says Dr. Cassady.

This means that people who spend minimum time chewing or even swallowing big chunks of food may have a hard to absorb nutrients from this food.

Is it bad to swallow big chunks of food?

“Swallow big chunks of food can interfere with gastric acid secretion and limits the accessibility of nutrients,” says Dr. Cassady.

“Chewing food helps to reduce particle size before swallowing and ensures sufficient food digestion.”

Although I don’t eat much lately, I noticed that chewing my meals for longer helps me to reduce my appetite and lower overall food intake (without even realizing it). I also tend to feel full for longer.

How to eat slower?

Are you a fast eater? Here are easy-to-follow steps that can help you slow down at your next meal.

1. Put down your fork or spoon in between bites

When you’re eating, it’s important to

Putting down your utensils in between bites not only helps you eat more slowly, but also gives your brain a chance to register that you’re getting full.

If you make a conscious effort to put your fork or spoon down between bites, you’ll find that you’re able to better tune into your hunger cues and are less likely to overeat.

2. Chew each bite thoroughly before swallowing

Chewing food thoroughly helps to break it down into smaller pieces, making it easier for your stomach to digest.

Plus, chewing stimulates the production of saliva, which contains enzymes that help to break down carbohydrates and fat.

3. Avoid distractions

Whenever you sit down to eat, it’s important to give your full attention to the meal. Turn off the TV, no scrolling through social media, and no work emails.

Distractions like these can make you eat mindlessly (eating more than you intended) and prevent you from fully enjoying your dish.

4. Eat when really hungry

One thing that made a huge difference in my own transformation was to make sure I’m really hungry before starting to eat.

I find that when I wait for a little longer for my meal, I can not only eat less but also enjoy it more.

Lessons learned

It took me several months to realize that eating fast makes me hungry sooner, and want to eat more (especially foods that I should not eat.)

On the contrary, eating slower does make you fuller because the longer you chew, the more it provides sensory output with all information about the food.

If you do not chew your food properly, it will not be digested well. Chewing makes it easier for your stomach to digest food, and also helps to break down food so you can get nutrients from it.

Michal Sieroslawski

Michal is an exercise physiologist (MSc) and a veteran endurance athlete. He loves to experiment and share his successes and failures to help busy men and women who want to lose weight.

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