Humans cannot digest cellulose, the main component of plant cell walls, because we lack the enzyme cellulase, making it dietary fiber that aids digestion but isn't broken down for energy, along with indigestible materials like rocks, plastic, metals, and certain fats, tough meats, and highly processed foods that are difficult for our bodies to process.
What can humans NOT digest?
10 Worst Foods for Digestive Health
Insoluble fiber is what we think of as roughage. This is the material from food that your body cannot break down in digestion, so it leaves the body pretty much as it goes in. Foods high in insoluble fiber include: Skins and seeds of fruits and vegetables.
The Correct answer is Cellulose. Cellulose is a type of complex carbohydrate or polysaccharide that is found in the cell walls of plants. Humans cannot digest cellulose because their digestive system lacks the necessary enzyme called cellulase to break down cellulose into glucose.
The hardest foods to digest are typically fried and fatty foods, processed foods, and some proteins like red meat, beans, and dairy (especially for lactose-intolerant individuals), along with high-fiber items like whole grains, cruciferous vegetables (broccoli, cabbage), and nuts/seeds, due to fat slowing digestion or fiber/complex carbs causing fermentation, gas, and bloating. Corn, spicy foods, onions, and caffeine can also be tough on the gut.
A peanut butter and jelly sandwich (PB&J) adds about 33 minutes to your healthy lifespan per serving, according to a University of Michigan study that measured life expectancy impacts of over 5,850 foods using the Health Nutritional Index (HNI). This sandwich tops the list for adding time, with nuts and seeds also being highly beneficial (around 25 mins) and processed items like hot dogs subtracting time.
In The Article
The covering of each delicious kernel of corn is insoluble. This is the undigestible kind that the body cannot break down and that passes through the body more or less intact, which can add bulk to bowel movements and ease constipation.
Refer to our article Restoring Intestinal Floral Leads to a Healthy Gut and Happy Poop for more information on the topic.
There's no single "number 1" unhealthy food, but ultra-processed items like sugary drinks, processed meats (bacon, hot dogs), deep-fried foods (fries), and refined snacks (donuts, chips, sugary cereals) consistently top lists due to high sugar, salt, unhealthy fats, and additives linked to obesity, heart disease, and diabetes. These items offer little nutritional value while increasing risks for chronic diseases.
Red meat, like beef or pork, can be difficult to digest for people of any age, but it may become more taxing as we get older. The body requires more digestive enzymes to break down red meat, which is naturally tough and protein-rich.
Eating easy-to-digest foods can help during an illness or a GI condition flare. Easily digestible foods include bananas, baked skinless poultry or fish, white rice, broth, herbal teas, and more, but what's easy for one person to digest may be different from what works for the next person.
Here are a few to keep an eye on:
The easiest foods to digest
The hardest foods to digest are typically fried and fatty foods, processed foods, and some proteins like red meat, beans, and dairy (especially for lactose-intolerant individuals), along with high-fiber items like whole grains, cruciferous vegetables (broccoli, cabbage), and nuts/seeds, due to fat slowing digestion or fiber/complex carbs causing fermentation, gas, and bloating. Corn, spicy foods, onions, and caffeine can also be tough on the gut.
As the popcorn is digested, the microbiome responds by greatly increasing its production of butyrate, a “short-chain” fatty acid that boosts human health in major ways.
Foods that can be inflammatory - Highly processed foods, like corn chips, fried foods and too much red meat, sugar, wheat, rye and barley in people with gluten allergies of celiac disease.
Foods that are high in polyunsaturated fats. To enhance the effectiveness of killing Helicobacter pylori bacteria in the stomach, patients should focus on supplementing foods rich in healthy fats, especially polyunsaturated fats omega-3 and omega-6, such as: Virgin olive oil, canola oil and sunflower oil.
The 7 Day Gut Reset is a clean-eating and lifestyle-based plan designed to: Eliminate common gut disruptors. Introduce healing, nourishing foods. Support your digestive system with hydration and rest. Improve the diversity of your gut bacteria.
Studies suggest that rice is completely absorbed in the small bowel, produces little intestinal gas and has a low allergenicity. Several clinical studies have demonstrated that rice-based meals are well tolerated and may improve gastrointestinal symptoms in functional gastrointestinal disorders (FGID).
What food can you survive on forever? No, it is not possible to survive on a single food forever without developing nutritional deficiencies. While some foods offer a broad range of nutrients, none provide all the essential macronutrients, vitamins, and minerals needed to sustain long-term health.
The 2-2-2 food rule is a simple guideline for leftover safety: get cooked food into the fridge within 2 hours, eat it within 2 days, or freeze it for up to 2 months to prevent bacteria growth, keeping it out of the temperature "danger zone" (40-140°F or 5-60°C).
Understanding the 3-3-3 Rule
Specifically, the rule suggests: Three balanced meals per day. Three hours between each meal. Three hours of movement per week.