Weight gain can be extremely frustrating, especially when you don't know what's causing it.

Although diet generally plays the biggest role in weight gain, other factors, such as stress and lack of sleep, can also contribute.

Here are 9 causes of unintentional weight gain.

1. You eat too many highly processed foods

Many healthy foods, such as oats, frozen fruit, and yogurt, are minimally processed.

However, highly processed foods, including sugary cereals, fast foods and microwave dinners, contain a host of harmful ingredients, as well as added sugars, preservatives and unhealthy fats.

Additionally, many studies link highly processed foods to weight gain, in addition to rising obesity rates in the United States and around the world (1).

For example, a 2019 study of 19 Canadian adults found that those who ate the most ultra-processed foods were 363% more likely to be obese than those who ate the least (32).

Highly processed foods are typically high in calories but lacking in essential nutrients, such as protein and fiber, that make you feel full.

In fact, in a two-week study of 20 people, participants consumed about 500 more calories per day on an ultra-processed diet than on an unprocessed diet (3).

So, you should consider cutting out processed meals and snacks, focusing instead on whole foods.

2. You eat too much sugar

Sweet foods and drinks like candy, cakes, soda, sports drinks, ice cream, iced tea, and sugary coffee drinks can easily enlarge your waistline.

Many studies link sugar consumption to weight gain, but also an increased risk of chronic diseases, including type 2 diabetes and heart disease (4).

In particular, sugary drinks are the leading source of added sugar in the United States and are closely associated with weight gain.

For example, a review of 30 studies involving 242 children and adults linked sugary drink consumption to weight gain and obesity (352).

A study of 11 women found that drinking one soda a day led to a 218-pound weight gain over 2,2 years, meaning cutting out candy could have the opposite effect ( 1).

You can try gradually reducing your sugar intake to make the process easier.

3. You have a sedentary lifestyle

Inactivity frequently contributes to weight gain and chronic disease (8, 9, XNUMX).

Working at a desk, watching television, driving a vehicle, or using a computer or telephone are sedentary activities.

A study of 464 obese and overweight people showed that their daily sitting time averaged 6,2 hours on workdays and 6 hours on other days. Work-related tasks were the biggest contributor, followed by television (ten).

Making a few simple lifestyle changes, such as exercising less and sitting still, can make a big difference.

For example, a three-month study of 317 workers showed that replacing one hour of sitting with one hour of standing all day reduced total fat mass and waist circumference while increasing lean muscle mass (11). .

Research has also shown that spending too much time in front of a screen significantly contributes to unintentional weight gain (12, 13, 14).

Even small adjustments, such as walking after dinner instead of watching TV, exercising or walking during your lunch break, investing in a standing desk or treadmill, or cycling to work, can counteract weight gain.

4. You engage in yo-yo dieting

Yo-yo dieting refers to cycles of intentional weight loss, followed by unintentional weight gain.

This trend is notably linked to an increased risk of weight gain over time (15, 16).

In a study of 2 people, people who had dieted in the past year had higher body weight and waist circumference than non-dieters (785).

Other studies reveal that restrictive dieting and dieting can lead to future weight gain due to your body's physiological reactions to such behaviors, such as changes in hunger and fullness hormones (18, 19). , 20).

Additionally, most people who lose weight while following a restrictive diet regain all or all of it within 5 years (15).

To lose weight long-term, you need to focus on sustainable lifestyle changes. These include exercising, cutting out processed and sugary foods, and eating nutrient-dense whole foods high in fiber and protein.

5. You have an undiagnosed medical problem

Although many lifestyle factors contribute to unintentional weight gain, certain medical conditions can also play a role. These include:

• Hypothyroidism. This condition affects your thyroid gland and can lead to weight gain or difficulty losing weight (21, 22).
• Depression. This common mental state is linked to weight gain and obesity (23, 24).
• Polycystic ovary syndrome (PCOS). PCOS is marked by hormonal imbalances that affect women of childbearing age. This can lead to weight gain and make it difficult to lose weight (25).
• Binge eating disorder (BED). BED is classified based on recurring episodes of uncontrollable overeating and can lead to many health complications, including weight gain (26).

Other conditions, such as diabetes and Cushing's syndrome, are also associated with weight gain. It is therefore important that your doctor makes the correct diagnosis.

Additionally, certain medications, including antidepressants and antipsychotics, can cause weight gain. Talk to a healthcare professional if you think you are gaining weight because of your medications.

6. You don't get enough sleep

Sleep is essential to overall health and well-being. Insufficient sleep can lead to weight gain, among other negative effects (27).

A study of 92 women showed that those who slept less than 6 hours a day had the highest body mass index (BMI) and levels of visfatin (a protein secreted by fat cells), compared to women sleeping 6 hours or more per day (28).

In a 2-week study of 10 overweight adults after a low-calorie diet, those who slept 5,5 hours per night lost 55% less body fat and 60% more muscle mass than those who slept 8,5 hours per night. hours per night (29).

As such, increasing your sleep time can help with weight loss.

Some evidence associates seven or more hours of sleep per night with a 33% greater likelihood of weight loss, compared to sleeping less than seven hours (30).

If your sleep quality is poor, you can try limiting screen time before bed, reducing your caffeine intake, and going to bed at a regular time.

7. You're not eating enough whole foods

If you regularly eat processed foods, switching to a diet richer in whole foods is a simple and effective way to promote weight loss and improve many other aspects of your health.

In fact, the most important factor in weight loss is choosing whole, minimally processed foods.

One study divided 609 overweight adults into groups who followed a low-fat or low-carb diet for 12 months (31).

Both groups were instructed to maximize their vegetable intake, limit their intake of added sugars, trans fats, and refined carbohydrates, eat primarily whole, minimally processed, nutrient-dense foods, and prepare most meals at home.

The study found that people in both diet groups lost weight similarly: 5,4 kg (12 pounds) for the low-fat group and 5,9 kg (13 pounds) for the high-fat group. low carb. This demonstrated that diet quality, not macronutrient content, was the most important factor in weight loss (31).

Incorporating whole foods into your diet doesn't have to be difficult. Start by slowly adding nutrient-dense whole foods, such as vegetables, fruits, beans, eggs, nuts and seeds, to your meals and snacks.

8. You are stressed

Chronic stress is a common problem that can affect your weight (32).

High levels of the stress hormone cortisol have been shown to increase hunger and your desire to consume highly palatable, high-calorie foods, which can cause weight gain (33).

Additionally, studies indicate that obese people have higher cortisol levels than those without the condition (34).

Interestingly, managing stress can promote weight loss.

In an 8-week study of 45 adults with obesity, those who practiced relaxation techniques like deep breathing lost significantly more weight than those who received only standard dietary advice (35).

To reduce stress, try incorporating evidence-based relaxation practices into your routine. Yoga, spending time in nature and meditating (36, 37, 38).

9. You eat too many calories

Overeating remains a significant cause of weight gain.

If you take in more calories than you burn per day, you will likely gain weight (39).

Mindless eating, regular snacking, and making dietary choices high in calories and nutrients all contribute to excessive calorie intake.

It can be difficult to determine your calorie needs on your own, so consult a dietitian if you have difficulty overeating.

Simple ways to avoid overeating include paying attention to hunger and fullness cues by eating wisely, following a diet high in fiber and protein, rich in plant foods, drinking water at instead of high-calorie drinks and increasing your activity level.

The bottom line

Many factors can contribute to unintentional weight gain.

Lack of sleep, sedentary activities, and excessive consumption of processed or sugary foods are just some of the habits that can increase your risk of weight gain.

However, a few simple steps – eating healthy, exercising and focusing on whole foods – can help you achieve your weight loss goals and improve your overall health.