Most people tend to associate a vegan diet with being lean. And science backs that notion. In a study of 40,000 adults, Oxford University researchers found that meat-eaters had the highest BMIs; vegans had the lowest; and vegetarians and semi-vegetarians landed somewhere in-between. But throughout my years in private practice, I've worked with plenty of clients who did not lose weight after cutting out animal products. And some even gained weight. Here are five common reasons this happens, plus how to avoid them—so you can reap both the health and weight-loss benefits of going vegan.
Your portions are too big
Healthy foods—including veggies, fruit, whole grains, nuts, seeds, and avocado—contain raw materials that either fuel the activity of your body's cells, or help maintain, heal, or regenerate tissue (such as hair, skin, immune cells, and muscle). But we don't require an unlimited supply of these nutrients. The amount your body needs is largely based on your age, sex, height, ideal body weight, and physical activity level. A young, tall, active man with a higher ideal weight, for example, requires larger portions than an older, petite, sedentary woman.
Often when I evaluate clients' food journals, I find that they aren't losing weight because their nutrient intake exceeds their needs. I had one female client who was eating a large açaí bowl for breakfast that contained multiple servings of fruit, nut milk, nut butter, and seeds. She would then commute by car to work and sit at a desk all morning. While the bowl was chock-full of nutrition, it packed about three times what her body actually needed to keep her satiated until lunch.
You aren't getting enough protein
Eating an adequate amount of protein is key for maintaining muscle mass, which helps keep your metabolism revved. It's possible to meet your daily protein needs on a plant-based diet. You just have to be strategic.
One of my clients who was struggling to drop weight (and feeling tired all the time) after he went vegan was surprised to learn he was only consuming about half the protein he needed. Most vegans I work with need at least 60 grams of protein per day. But many don't know if they're hitting that quota.
To make sure you're getting enough, try tracking your intake (even briefly) with an app like My Fitness Pal. Another strategy is to include more pulses (the umbrella term for beans, lentils, and peas) in your meals, since they are one of the best sources of plant protein. One cup of cooked lentils contains 17 grams of protein, compared to about 8 grams in a cup of cooked quinoa or a quarter cup of almonds. Whipping a plant-based powder (such as pea protein, made from yellow split peas) into a smoothie can also boost your intake, by as much as 25 grams per serving.
Your timing is off
Whether you're a vegan or an omnivore, meal timing can have a serious impact your waistline. Many people I talk to eat their largest meal in the evening, when they're the least active. A smarter strategy is to eat larger meals earlier, so they fuel your most active hours of the day.
Skimping all day and gorging at night is a recipe for weight gain, or at least preventing weight loss-even if you're vegan. Try switching to evening meals that are filling but but light, such as sautéed veggies and chickpeas over a bed of greens and spaghetti squash; or a broth-based veggie and white bean soup with a drizzle of EVOO.
You're eating plant-based junk food
I've had plenty of clients who believed it was okay to eat unlimited amounts of plant-based treats (think coconut milk ice cream and sweet potato chips). Plant-based frozen foods, desserts, and snacks can not only be high in calories, but they're often made with refined flour and added sugar, and stripped of nutrients and fiber. While they're fine as occasional treats, when consumed daily, they can pack on pounds. One study found that processed foods may decrease post-meal calorie burning by nearly 50% compared to whole foods. Trade processed plant foods for fresh snacks. Reach for in-season fruit and dark chocolate to satisfy a sweet craving; and raw veggies with hummus or guacamole for a savory fix.
You're drinking too many calories
There are many beverages marketed to plant-based consumers: kombucha, drinking vinegars, green juices, chia drinks, coconut water, and almond milk cold brew coffees, just to name a few. With so many choices, I've seen many clients unknowingly sip hundreds of extra calories per day.
My rule of thumb is this: If it's not water or unsweetened tea, your beverage should count as part of your meal or snack. One vegan client who found she wasn't losing weight was drinking a smoothie along with her lunch salad. Unknowingly, she was essentially consuming two lunches every day. Another client didn't realize that the healthy (and expensive) beverages she drank twice a day in lieu of soda contained about 300 calories total. That may not sound like a ton, but it would take a one-hour speed walk to burn off just those drinks.
Make good old H2O your drink of choice, and if you reach for anything else, take a careful look at the ingredients, nutrition facts, and serving size, so you can decide if it's the best fit for your body's needs.
Cynthia Sass is Health's contributing nutrition editor, a New York Times best-selling author, and consultant for the New York Yankees. See her full bio here.