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Why Am I Gaining Weight on a Diet?

By Elisa Hoffman

Reviewed by Briana Rodriquez, R.D.


Updated: October 13, 2022


You’re cruising along in your weight loss journey, and the pounds are coming off every week. You feel great! And then, seemingly out of the blue, you stop losing weight. Or worse, you start gaining weight. You're on a diet, how is this unexpected weight gain possible? It’s not like you’re doing anything differently ... or are you? The frustrating question screams out: Why am I gaining weight on a diet?


Here’s a rundown of nine potential reasons why you could be eating healthy and exercising but are seeing your weight increase, and what you can do to reverse the frustrating trend of dieting but gaining weight.


#1. You’re eating too much (and might not know it)

042618_PortionControl_Main_Updated.jpgWhether you’ve just started a weight loss program or you’ve been on a weight loss journey for a while, life happens. Maybe you were too exhausted after a long day at work to prepare a healthy meal, so you grabbed some fast food on the way home instead. Or you went out to eat with your friends and the menu options were less than stellar (hello, bottomless bread basket!). Whatever the case may be, scenarios like this pop up from time to time that can be difficult to navigate when you’re on a diet.


If you’re eating out frequently, “portion distortion” — being served more than the recommended serving size (and possibly eating more than you intend to) — could be causing extra weight gain. Also, takeout meals usually have more fat and calories in a standard dish due to how the food is prepared (think: fried food).


The problem with "portion distortion" is that you may order a meal and think, "Great, here’s one portion." But remember: a portion size is the amount you decide to eat, while a serving size is the measured amount that is recommended for consumption. A serving size also represents quantities on a nutrition facts label. Most restaurants often prepare meals that may have two or even three servings in one portion. And it's hard to recognize because portion sizes have become so inflated over recent years. In fact, the average size of most meals from fast-food chains and sit-down restaurants has grown by as much as 138% since the 1970s.1


Because of how standard U.S. food portion sizes have grown, it’s important to familiarize yourself with proper portion sizes and pay attention to how much food you’re eating. One way to do this is to focus on filling your plate with non-starchy vegetables first and then selecting a protein and carbohydrate source to balance your meal. MyPlate is an excellent resource that follows Dietary Guidelines to divide your plate by food group as well as provides visual cues so you know exactly how much to put on your plate. Or, use this visual portion infographic to help guide your portion sizes. Not watching your portion sizes could be one of the reasons why you are gaining weight while dieting.


Another way to monitor your portions is through mindful eating. Taking the time to notice your hunger cues and stop when you feel satisfied, not completely full, may help you avoid overeating. Part of mindful eating is enjoying the textures, smells and tastes of your food by slowing down and savoring each bite. By taking your time, you're giving your body the time it needs to communicate to your brain feelings of fullness.  Browsing through all of the possible intermittent fasting meal plans and beginning one can help with overeating.


Need some more tips to eat healthily when dining out? Check out this helpful guide.

#2. You're not eating enough


WhyAmIGainingWeight_NotEnoughFood.jpgYou may be thinking wait — not eating enough can make me gain weight? Even on a diet? Turns out, it can, especially if you’re reaching for the wrong kinds of foods.


Skipping meals can cause you to get extremely hungry and stray from your planned healthy meals and snacks. So you may be tempted to grab whatever is nearby to satisfy your hunger — including junk food that may be high in fat and sugar that don’t support your diet or weight loss goals.


One way to avoid this from happening and to properly know how often you should eat is to make sure your body is properly nourished by preparing healthy snacks to eat throughout the day. Eating snacks cannot only help you manage your hunger, but healthy snacks may also help prevent eating large quantities of food later on. However, snacking doesn't mean you should grab potato chips and cookies. You’ll want to opt for low-calorie, nutrient-rich options that will not only give you energy but will nourish your body and support your weight loss goals.


Which snacks are healthiest? Here are a few things to look for when choosing your next snack. First, opt for something that is nutrient-rich (the quality of your snacks matter!) — a few of our favorites include veggies and a tablespoon of hummus, a piece of fruit like a small apple or a handful of berries. Next, choose a snack with fiber, which can help fill you up.2 Air-popped popcorn, a pear, a cup of carrots, baked broccoli and other non-starchy vegetables are all great options. In addition, it is important to make sure your snack has adequate protein. For example, nuts are a great choice when eaten in moderation; they are high in fiber, protein and healthy fat. Other healthy options include non-fat plain Greek yogurt, reduced fat cheese, edamame and avocado.


Just remember to keep an eye on your portion sizes! This will help you stay on track with your weight loss goals, so that you can avoid weight gain on a diet.


Here's how smart snacking may boost your weight loss. Plus 9 healthy snack ideas!

#3. You're consuming too much sodium 

Your body is comprised of mostly water and can sometimes hold onto excess water. If you’ve consumed too much salt — whether it’s from using the table salt at dinner or from eating unhealthy processed foods (like salty chips) — your body can retain water to help maintain a chemical balance.


WhyAmIGainingWeight_WaterRetention.jpgFor women, your menstrual cycle may lead your body to retain enough water to show up on the scale. Sodium can aggravate the issue, so keep a close eye on your salt intake and make sure you are properly hydrated (Use these 10 tips to start drinking more water every day). 


If you find yourself gaining weight while dieting, you may want to take a look at your sodium intake. This includes not only using less salt at the table, but also reducing your intake of certain high-sodium foods like baked goods, certain lunch meats (think: sausages, hot dogs and cold cuts), salted nuts and greasy potato chips. Check the labels when buying a product, and you might be surprised to find how much sodium is in everyday foods.


So, what should you eat instead? Good alternatives include fresh and frozen meat, fresh or frozen vegetables (instead of canned), unsalted nuts or low-sodium nut butter. Eating more whole foods in their natural state or those you prepare yourself is a great way to avoid too much salt.   


In addition to cutting down on sodium, you might also want to try increasing your intake of foods rich in potassium, which may help to alleviate water retention.3 Some foods rich in these nutrients include leafy greens, whole grains, avocados and tomatoes.


Monitoring your food intake and drinking plenty of water may help you get back on track with your weight loss goals, and halt putting on weight while dieting, if you’ve been consuming too much sodium.


#4. You're building muscle 

Prior to starting your weight loss journey, did you follow a regular exercise program? If not, consider it! Working out could help you lose some body fat and gain muscle mass. By incorporating strength and cardiovascular exercise into your routine, research suggests that you may experience increased fat loss as well as weight loss.4 While a pound of muscle and a pound of fat weigh the same, muscle occupies less space, so it could cause the number on the scale to stall even though your body composition is changing.


WhyAmIGainingWeight_Muscle.jpgOne sign that this could be true for you: Your weight holds steady or goes up a pound, but your clothes keep getting looser. That’s why it’s important to not only monitor your body weight but also your measurements to get the entire picture!  


Developing lean muscle mass is not only healthy —  having more muscle will slightly increase how many calories you burn, even when you’re at rest.5 Research from The Journal of Strength and Conditioning Research found that women who completed an hour-long strength training workout burned an average of 100 more calories in the 24 hours afterward than those who didn’t use weights.6


But there are health benefits beyond weight loss and toned muscles that strength training can deliver: Research suggests that muscle strengthening exercises may improve your blood sugar control, improve your heart health, improve your balance and even help prevent osteoporosis.7


Picking exercises you enjoy can help you get lean while also getting stronger. Some good choices include running, high-intensity interval training, swimming, lifting weights, rowing, Pilates, and more. Not sure where to start? Check out these 6 tips to start a strength training routine.


In the long run — having more muscle will support your weight loss efforts and actually may prevent you from gaining weight in the future. 


Reclaim a Healthier, Happier You with Jenny Craig

#5. You're drinking unhealthy drinks

WhyAmIGainingWeight_Soda_Resized.jpgWhen people decide to make a lifestyle change, they often think about how to eat healthier and exercise more, but they tend to forget about what they are drinking. However, it is important to pay attention to the beverages you are consuming because plenty of drinks can be unhealthy and loaded with calories that can derail your weight loss goals.


For starters, most of us know that drinks like soda are laden with sugar and can cause weight gain. But energy drinks and juices can also be culprits. These drinks should be limited or consumed in moderation, not with every meal. Alcohol is another drink that many people forget is filled with calories. You might think you’re cutting calories at happy hour by having two glasses of red wine instead of opting for a high-calorie mixed cocktail, but those two drinks still add approximately 300 additional calories to your day.8 That’s the same as if you had snacked on three small chocolate chip cookies!9 


Instead of relying on sweetened drinks or beverages, stick to water, soda water, or other drinks for weight loss assistance. Not only is it calorie-free, but it can also help fill you up10 and keep you energized. A general rule of thumb is to drink at least eight 8-ounce cups of water a day. Everyone’s water consumption needs vary — so it’s important to take into account your activity level, the climate and your thirst. If you're craving something sweet, add a splash of lemon or lime juice to give your water a little more flavor.



NewYear_sleep.jpg#6. You're not getting enough sleep

It might seem like your sleep habits have nothing to do with your weight, but there is a link between the two and lack of sleep could be the reason you're gaining weight while dieting. Feeling tired isn’t the only side effect of sleeplessness. When you don’t sleep well, your body can crave junk food rather than the healthy meal you had planned. Research suggests that getting less than five hours a night could increase appetite and have a negative impact on your metabolism.11


To avoid messing with your body’s hormones and consuming foods that will not serve your health needs, you’ll want to make sure you get enough sleep. The National Sleep Foundation recommends that adults between 26-64 years old should aim to get 7-9 hours of sleep each night.12

#7. You're too stressed

MonitorYourStress_React.jpgHad another stressful day at work? While small stressors are common in everyday life, experiencing constant stress isn’t beneficial for your health. In fact, chronic stress may be one of the reasons you’re gaining weight on a diet. Why? For starters, people often turn to unhealthy foods when they’re stressed. Cortisol, the hormone that is naturally released during stressful situations to help fight inflammation, may cause strong cravings for high-fat, sugary foods. What’s more, research has linked long-term levels of elevated cortisol to obesity.13


Combat stress-induced weight gain by having some go-to stress-relieving hobbies like exercising, spending time with family and friends, doing yoga, working on a craft or reading. Turn to these activities instead of heading to the pantry for some healthy stress relief.

#8. You're getting older

Your age is another factor when it comes to the growing number on the scale. Unfortunately, as you age, your metabolism is not as efficient and you can start to burn fewer calories.14 Additionally, women who have reached menopause often experience weight gain.


Just because you’re getting older, doesn’t mean you’re stuck at an unhealthy weight forever. Healthy eating and exercise can help. Take a careful look at your diet and see if there is anything you are doing that may be contributing to weight gain. For example, do you find yourself snacking late at night? What about eating too much sugar? By pinpointing any unhealthy behaviors, you may be able to get back on track and reverse unwanted weight gain.


Learn more about diet changes to make at age 40 and beyond.

#9. You're not exercising enough

LongSummerDays_Exercise.jpgEven though eating healthily by consuming plenty of vegetables, fruits and whole-grains is the key to reaching your weight loss goals — if you’re not getting up and moving, you might not see the weight loss you desire. The Centers for Disease Control and Prevention (CDC) recommends getting at least 150 minutes of moderate aerobic activity or 75 minutes of vigorous aerobic activity per week.15 Additionally, the CDC recommends that you aim to incorporate at least two days a week of strength training activity. (New to exercise? Check out our Beginner’s Guide to Exercise.)


Physical activity does more than help you burn calories: It can also benefit your mental health and motivate you to make healthier choices in other areas of your life.16 If you’re just getting started with exercise, you don’t have to jump right into a CrossFit class. Start with a simple walking and stretching routine. Or if you love dancing, take a class at your local dance studio. It’s a great way to get moving, have fun, and do something you love. Plus, it can be a fun and healthy activity to do with friends instead of happy hour or going out to eat.


There are a lot of factors when it comes to weight loss and weight gain, but the healthier your lifestyle habits are, the better results you’ll see. We hope we’ve given you some insight into why you may be gaining weight while dieting. Hopefully, these tips will get you back on the right track and moving toward your weight loss goals!


Need some help reaching your weight loss goals? Book a free appointment with a weight loss coach and discuss your goals! 




Elisa Hoffman

bio-photo-Elisa.jpgElisa is a content marketing manager for Jenny Craig with over ten years of experience working in the health and fitness industry. She loves sharing her passion for living a balanced and healthy lifestyle. A San Diego native and an endurance sports enthusiast, you can usually find her swimming, biking along the coast highway or running by the beach in her free time. Elisa holds a Bachelor of Arts degree from California State University, Chico.


Favorite healthy snack: mozzarella string cheese with a Pink Lady apple



Reviewed by Briana Rodriquez, RDN

bio-photo-briana.pngBriana is a Registered Dietitian Nutritionist and Certified Personal Trainer for Jenny Craig, based in Carlsbad, California. She is passionate about utilizing food as functional and preventative medicine. Guided by a simplistic and optimistic approach, Briana’s philosophy is to help people improve their health and achieve their goals through the development of sustainable habits to live a healthy life. In her free time, you can find her strength training, indoor cycling, coffee tasting, and at local eateries with her husband and two dogs.


Favorite healthy snack: peanut butter with celery alongside a grapefruit-flavored sparkling water (so refreshing!)





This article is based on scientific research and/or other scientific articles and was written by an experienced health and lifestyle contributor and fact-checked by Briana Rodriquez, RDN, Registered Dietitian Nutritionist at Jenny Craig.


Our goal at Jenny Craig is to provide the most up-to-date and objective information on health-related topics, so our readers can make informed decisions based on factual content. All articles undergo an extensive review process, and depending on topic, are reviewed by a Registered Dietitian Nutritionist (RDN) or Nutritionist, to ensure accuracy.


This article contains trusted sources including scientific, peer-reviewed papers. All references are hyperlinked at the end of the article to take readers directly to the source.






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