Eat Onions every day for Weight Loss

Eating a tomato salad with raw onions before a high-calorie meal is good for weight loss. Onions regulate appetite with only a few calories. Also, they burn belly fat, as they’re high in:

  • fiber
  • water
  • flavonoids
  • quercetin
  • vitamin C

Benefits for Weight Loss


Above all, onions are good for weight loss because they’re low in calories. Onions have about 40 calories per 100g. A medium onion has about 45 calories. All onion varieties have similar calories per 100g:[1]

  • red onions have 42–44 calories
  • yellow onions have 36–38 calories
  • white onions have 33–36 calories

Young green onions have fewer calories than onion bulbs. They have only 27 calories per 100g. A cup of young green onions has 20 calories.

Sautéed onions have 123 calories per 100g. A cup has 107 calories.

French onion soup is also high in calories. It has 154 calories per 100g. A cup has 371 calories.

Above all, onion rings are fattening! They have too many calories. Onion rings have 411 calories per 100g. A small 1 oz serving has about 120 calories.


Moreover, onions reduce hunger, as they’re high in fiber. They contain between 1.2 and 2.2 grams of fiber per 100g, depending on the variety.

  • White onions have the lowest fiber content (1.2 grams per 100g). A medium onion contains about 1.7 g of fiber or 5% of the recommended daily intake.
  • Yellow onions have a medium fiber content (1.9 grams per 100g). A medium yellow onion contains 2.7 g of fiber which is almost 8% DV.
  • Red onion is the richest variety in fiber (2.2 grams per 100g). They have almost twice the fiber content as compared to white onions! A medium red onion contains about 3.1 grams of fiber or 9% DV.
  • Onion greens are also excellent dietary sources of fiber, with 2.6 grams per 100g.

The main types of fiber in onion are cellulose and pectic polysaccharides. Storage of onions increases their insoluble fiber content.[2,3]

Fiber occupies a significant amount of space in the stomach. Also, it slows down digestion. Thus, onions have a huge satiating effect. They can significantly reduce energy intake, as they can keep you full for hours! A caloric deficit is crucial for weight loss.

As a rule of thumb, we should consume at least 28 grams of fiber on a 2,000-calorie diet. Lower doses increase the risk of obesity![4]

Furthermore, onions have prebiotics, which are a type of fiber. We can’t digest prebiotics. But, the beneficial bacteria in the gut eat them! So, onions support a healthy digestion system, which is beneficial for maintaining an ideal body weight. Also, the regular consumption of onions can prevent nonalcoholic fatty liver disease.[5]

Low in Sugar

Most calories of onions come from sugars. White, yellow, and red onion varieties have approximately 5.76 grams of sugar per 100g. A medium onion has about 8.2 grams of sugar.

Onion greens have the least amount of sugar, though. They contain only 2.3 grams of sugar per 100g.

People who follow a ketogenic diet shouldn’t consume more than 20-50 g of carbs a day. As onions have fewer than 10 g of carbs per 100g, people who follow a ketogenic diet can consume them in moderation.[6]

People with diabetes can eat onions as well as other non-starchy vegetables, like tomatoes, squash, carrots, beets, broccoli, eggplant, asparagus, kale, as well as collard, mustard, and turnip greens.[7]

Onions may help people with diabetes lower their blood glucose and cholesterol levels.[8,9,10]


Furthermore, onions hydrate us, as they’re 90% water. We should be properly hydrated in order to burn more belly fat while dieting. Water is necessary for the metabolism of fat.[11]

If you don’t like drinking tap water, you should at least consume lots of foods high in water, such as tomato, cucumber or watermelon. Most fruits and vegetables are high in water.

Moreover, onions hydrate better than tap water, as they have electrolytes. We have to replenish electrolytes daily for good health and to lose more belly fat. Electrolyte imbalances can impair fat metabolism.

Vitamin C

In addition, onions are a good dietary source of vitamin C. A medium onion has about 8.1 mg of vitamin C, or 9% of the DV. Vitamin C promotes weight loss and burns belly fat.

Flavonoids & quercetin

Most noteworthy, onions have an excellent antioxidant content. Actually, onions are among the richest natural sources of flavonoids. They’re the main source of flavonoids for most people.[12]

Onions have 34 phenolics. 17 of them are flavonoids. The richest and the most important flavonoid in onions is quercetin (37%).[13]

Quercetin has potent anti-obesity effects. It can improve body composition in overweight people. Additionally, quercetin may lower blood glucose levels.[14]

Moreover, antioxidants in onions fight inflammation and neutralize free radicals. High amounts of free radicals lead to oxidative stress, which can make you gain weight.

The best sources of flavonoids and polyphenolic compounds are fruits, vegetables, and beans.

How to eat onions for weight loss?

Onions are a key ingredient to countless food recipes. Not only do onions reduce hunger with only a few calories, but also they regulate the total glucose response of a meal.

As onions are pretty low in sugars, but high in fiber, vitamins, and antioxidants, they don’t spike blood sugar levels. Onions have an extremely low Glycemic Index of 15.[15]

Furthermore, as onions have a low glycemic index, even people with diabetes and people who follow a ketogenic diet can eat onions regularly.

As a rule of thumb, you should prefer consuming lots of foods with a low glycemic index if you want to lose weight. They burn belly fat and help maintain a healthy body weight.[16]

You can eat onions with foods with a high glycemic index, like pasta. They can substantially lower the total glycemic index of the meal. You can sauté onions with tomato sauce and dry herbs, like oregano! Spices are the richest foods in antioxidants. Antioxidants protect from chronic low-grade inflammation that causes obesity.

Sautéed or raw onions?

For an even higher satiating effect and a lower total glycemic index, you could eat raw onions with tomato, bell peppers, and cucumber. A tomato salad before a high-calorie meal is beneficial for weight loss! Furthermore, you can eat onions on an empty stomach, as they have a low glycemic index.

Don’t add too much olive oil. All vegetable oils are super calorie-dense foods. Just a tbsp has 125 calories!

Raw onions are better for weight loss than sautéed onions, as they have fewer calories. Sautéed onions have 220% more calories than raw onions!

Furthermore, heat can destroy quercetin and other flavonoids in onions. You should avoid cooking onions at temperatures higher than 150oC.[17]

Moreover, raw onions are more filling, as they have more water.

Above all, you shouldn’t discard the outermost layers of the bulb. They have the highest concentration of antioxidant compounds as compared to the middle and inner layers.[18]

Which onion variety is better for weight loss?

Red onions are slightly richer in antioxidants as compared to other varieties. For instance, red onions contain 415-1,917 mg of flavanols per kg. Yellow onions contain only 270-1,187 mg. White onions contain even lower concentrations.

Flavonoids give onions their distinct color. For instance, the anthocyanins are responsible for the color of red and purple varieties. On the other hand, varieties high in flavanols are yellow or brown.[19]

So, what’s the best onion variety for good health and weight loss?

You should eat whatever onion variety you like the most. Each variety has different concentrations of antioxidant compounds. Moreover, you could use all onion varieties in different food recipes.

Additionally, onions may help decrease cholesterol levels. Especially, red onions can significantly decrease LDL cholesterol. It seems that quercetin, the main antioxidant compound in red onions, is capable of altering the expression of genes involved in cholesterol metabolism! Also, it can increase blood HDL cholesterol levels.[20]

Furthermore, onions may improve the total metabolic status of the body. For instance, they can lower blood sugar and triglyceride levels.[21,22]

Does cooking affect the iron content of onions?

The cooking method doesn’t significantly affect the iron content of food. Iron and other minerals aren’t as vulnerable to heat as vitamins.[23]

Above all, you better use iron pots and pans to cook onions and other foods high in iron. Iron cookware can increase the iron content and the bioavailability of food.[24,25,26]

Onions are poor in iron. They have between 0.15 mg and 0.28 mg of iron per 100g. The iron content depends on the onion variety:

  • White onions have the lowest iron content.
  • Yellow and red onions are much richer in iron. They contain almost twice as much iron, as compared to white onions.
  • Onion greens have the highest iron content, though. They contain approximately 1.5 mg of iron per 100g!

We absorb only a small percentage of iron in onions, though. All plant-based foods have a low iron bioavailability. It’s estimated that we absorb only 5-12% of iron from plants.

In contrast, we absorb up to 18% of iron from animal-based foods.

We could increase the absorption of iron, by eating foods high in vitamin C. Vitamin C enhances iron absorption!

Also, animal-based foods, like meat, poultry, and seafood, enhance iron absorption.

Iron is vital for muscle metabolism, healthy connective tissue, energy metabolism, cellular functioning, physical growth, neurological development, and the synthesis of some hormones, amino acids, and collagen.[1,2]

Iron deficiency is the most common nutritional deficiency worldwide.

You can find a wide variety of iron pots and other cookware on Amazon.

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