How Long Will it Take Before You Start to See Effects of a Vegetarian Diet?

If you're going vegetarian or vegan, you're probably going to have a lot of people asking you the same thing over and over again — why? Although many vegetarians give up eating meat because they love animals, others do it because of the health benefits attributed to a plant-based diet.

It's true that vegetarians and vegans enjoy many positive parts to their new way of life, but they have to watch what they eat, or else they'll have some negative effects as well.

So if you've recently given up meat and are wondering how quickly you'll see a change — for better or worse — it's time to take a look at what you can expect.

Vegetarian is a flexible term that could refer to several types of diets. Some vegetarians eat eggs and milk products, or even fish, whereas vegans eat no animal products whatsoever (that means no meat, poultry, fish, dairy, eggs or even byproducts like gelatin and honey).

Those who cut back on, or cut out, meat may see benefits like lower blood cholesterol levels, lower blood pressure, lower intake of saturated fat, more vital nutrition, healthier body weight and a decreased risk of such conditions as type 2 diabetes, heart disease and certain cancers.

In its report "The Long-Term Health of Vegetarians and Vegans," Cambridge University noted that vegetarians tend to have good long-term overall health, and they have a lower chance of having some diseases and medical conditions, but more research is needed, especially in regard to the health of vegans.

Many of these benefits — especially a reduced risk of cancer — come from eating an abundance of vegetables and fruits, as vegetarians have an easier time getting their five servings a day. Those who eat a plant-based diet but include fish or poultry are usually just as healthy, and in some cases, pescatarians are at a lower risk of cancer than vegetarians, according to Harvard Health. Eliminating red meat, however, is important for lowering the risk of colon cancer.

Vegetarians do need to be careful about getting certain nutrients found in meat and dairy products, namely protein, iron, calcium, vitamin D, zinc, vitamin B12 and omega-3 fatty acids, as a lack of these could result in health problems (more on that later).

​Read more:​ 12 Tips to Getting a Vegetarian Diet Right

So how long until you feel the effects of a vegetarian diet? It depends on which effects you're waiting to see.

Some changes will be immediate, like the effect of fiber on your digestive health. The American Academy of Family Physicians recommends that if a sudden increase in fiber causes bloating, cramping or gas, you should increase your intake slowly over several days to a week so that your body can adjust.

Significant weight loss will take at least a few weeks or even months. In an April 2015 study published in the​ Journal of Pediatrics​, which involved only 14 families, doctors looked at both a vegan diet and the American Heart Association diet in regard to their effect on cardiovascular disease.

Although the statistical analysis of the study showed slightly lower body mass index (BMI) for children on a plant based diet, improved waist circumference was seen for children on the American Heart Association diet. Furthermore, cholesterol and blood sugar levels were improved in adults on a plant based diet, but not for children.

Plant based diets may be favorable in some regards, but not all. These markers were studied over the course of four weeks — these changes weren't observed in the course of a few days or even one week.

Another 2015 study, this one published in February in ​Nutrition​, assigned adults with overweight to one of five diets — vegan, vegetarian, pesco-vegetarian, semi-vegetarian or omnivorous — ultimately finding that vegan diets result in greater weight loss than the others. This weight-loss was observed over a six-month period of time.

A third review study from 2015, this one published in October in the ​Journal of the American Heart Association​, looked at several trails with an average duration of intervention of 24 weeks to determine the effect of vegetarian diets on blood lipids, ultimately finding that vegetarian diets lowered total, LDL, HDL and non-HDL cholesterol more than the control diets.

So although vegetarian diets can bring about positive changes, they don't happen overnight. It requires sticking to a diet over a period of time. Pay close attention to what foods you are eating and how they make you feel. With any diet, you need to wait at least two to four weeks to see how your new overall eating pattern is affecting you.

​Read more:​ Small Diet Changes that Yield Big Results

Just as there are with other diets, there are healthy and unhealthy versions of vegetarianism and veganism. Vegetarians who consume large quantities of processed foods instead of basing their diet on vegetables, fruits and whole grains can become nutrient deficient or have overweight.

A poorly planned vegan diet can also miss out on nutrients that are commonly found in meat, poultry and fish, which could cause such problems as anemia, loss of bone strength and neurological disorders. Contrary to popular belief, vegans are not necessarily deficient in protein intake or amino acid intake.

Even these negative health effects will take some time to manifest or alleviate. For example, someone who stops eating all meat and dairy might not consume enough vitamin B12, which is found only in animal products.

Unless this particular vegan starts getting vitamin B12 from fortified foods, such as breakfast cereal, he or she could become deficient. But vitamin B12 is stored in the liver, and it could take up to three years for the body to deplete its full store.

Similarly, if a vegan becomes anemic but then makes a conscious effort to start taking in more iron from plant sources — such as black beans, quinoa or soybeans — it will take three to four months to reverse that iron deficiency.

A big problem with deficiency in the vegetarian diet is simply the need to consume more. A September 2017 study published in the ​Journal of the International Society of Sports Nutrition​ examining the effects of a vegan diet on athletes pointed out that plant-based foods fill you up faster, so it becomes harder for a vegan to take in adequate calories.

Similarly, digestibility and absorption of protein, calcium, iron and zinc from plant sources is not as good as it is from animal sources, so vegans, especially physically active ones, need to consume higher amounts of these nutrients than they would if they were getting them from meat.

​Read more:​ A Vegetarian Diet Plan for Beginners

If you decide to go vegetarian or vegan, you likely will see a change in your body — whether that change is good or bad will depend on how much care you put into planning your diet. Pay close attention to the way you feel over the weeks after you make the change, and talk to your doctor, who can help you test for nutrient deficiencies.