Dieting and Immune Function

Review of J Am Diet Assoc. 2004;104(6):903-12.

A study in the Journal of the American Dietetic Association looked at how repeated weight loss and weight gain (weight cycling or 'yo-yo dieting') affects the immune system. In particular, the researchers studied a part of the immune system known as Natural Killer cells (NK cells). This study suggests that repeatedly losing and regaining weight, over time, decreases both the numbers and the effectiveness of NK cells in the body. In other words, weight cycling or 'yo yo dieting' appears to decrease at least one component of immunity in healthy people. We provide PRACTICAL information on what these findings mean. We provide ideas for how this information can be incorporated into a healthy dietary plan with the goal of minimizing cancer risk. This will provide useful information to people who are trying to use nutrition to reduce their risk of cancer.

Note: Numbers appearing at the end of sentences indicate research references. References are listed at the end of each article.

Background

Obesity (being significantly overweight) is linked with higher risk of many chronic diseases, including cancer, heart disease, diabetes, hypertension (high blood pressure), kidney disease, stroke, gall bladder disease and sleep disorders (1-10). The good news is that research also tells us that losing weight will lower these risks (11-15). In other words, if an overweight person successfully loses weight and keeps it off, many of these health risks decrease or disappear altogether. Unfortunately, some people who lose weight do not succeed in keeping it off. Instead, they go through many cycles of 'yo yo dieting' or losing and regaining the same weight over and over again (16-20).

Because losing and regaining weight is common, it is important for health researchers to understand the possible negative health effects of 'yo yo dieting'. A study in the Journal of the American Dietetic Association looked at how repeatedly losing and regaining weight affects immune system function (21). It is hoped that understanding the possible negative effects of repeated weight cycling will help people to be more motivated to develop a sensible weight loss plan that can keep them at a healthy weight permanently.

What The Researchers Studied

For this study, researchers collected information from 114 healthy women who were 50 to 75 years old. The women were asked about their weight and weight loss attempts over the course of their adult life. Information on other important factors, including medical history, exercise levels, use of dietary supplements (vitamins), current diet, and use of alcohol and tobacco (drinking and smoking) was collected and accounted for in the study. Researchers used all of this information to study whether repeatedly losing and gaining 10 or more pounds (lbs) by purposeful dieting had an effect on immune function. In particular, the researchers studied a part of the immune system known as Natural Killer cells (NK cells). Many researchers are especially interested in this type of immune system cell because NK cells play an important role in fighting cancer (22,23).

What The Study Found

First, the researchers found that women who reported losing 10 or more lbs intentionally (on purpose) one or more times in the past, had NK cells that were less effective than women who had never lost weight intentionally. In other words, when the researchers measured how well each woman's NK cells were functioning in their role in the immune system, women who dieted to lose weight in the past had NK cells that did not function as well.

Second, the researchers found that the more times in the past a woman had lost weight, the less effective her NK cells were. In other words, the more a woman 'yo yo dieted', the less healthy her NK cells were in their role in the immune system.

Third, the researchers found that the longer a woman had been at her current weight, the better her NK cells were functioning. In other words, being at a stable body weight, instead of 'yo yo dieting', appeared to improve the health and function of the NK cells in a woman's body.

Finally, the more often a woman had lost weight in the past, the lower the number of NK cells she had in her body. In other words, losing weight many times in the past ('yo yo dieting') decreased the number of NK cells in a woman's immune system.

What do these results mean?

If the women in this study are similar to most women, this study tells us that repeatedly losing and regaining weight over time, or 'yo yo dieting' may decrease immunity. In particular, the functioning of an important type of immune system cell that is known to help fight cancer is damaged by frequent weight cycling.

This study does have several weak points that we need to consider. This type of study cannot prove cause and effect; it only tells us that there is an association between 'yo yo dieting' and decreases in the numbers and effectiveness of one part of the immune system. It is important to remember that an association is not causation (cause and effect). It might be that there are other health factors associated with 'yo yo dieting' that account for these results.

As well, this study asked women detailed questions about their weight and weight loss attempts that had occurred in the past. This can create problems because sometimes people do not remember their diet and dieting attempts accurately, over time.

Finally, this study did not look at actual cancer risk. This study DOES NOT tell us that 'yo yo dieting' is linked with cancer. This is a very important point to keep in mind. This study does not suggest that 'yo yo dieting' causes cancer. Instead, it tells us that 'yo yo dieting' may damage one part of our immune system which is necessary to fight cancer.

However, the results of this study are important because they give us one more reason to work on getting to a healthy body weight and staying there.

In other words, even though this study doesn't directly relate to cancer, it does tell us that a part of our immune system that fights cancer can be negatively affected by losing and regaining weight over and over. In addition to this, the results do agree with other research that tells us that heavy dieting may decrease our immune system function (24-29).

Body Weight, Weight Management, and Cancer Risk Reduction

What should you do if you need to address weight loss and you want to keep your immune system functioning well? If you have a history of cancer, it is doubly important that you focus on getting to and maintaining a healthy body weight. Being overweight increases the risk of getting cancer again for several types of cancer, including breast and prostate cancers. But even if you do not have a history of cancer, being overweight increases your risk of getting this disease and many others.

It is important to make slow, steady, permanent weight loss a part of your commitment to better health. 'Yo yo dieting' is not the answer. Taking care of yourself with a sensible weight loss plan is the answer. And remember that it is never too late to start. Researchers have found that being significantly overweight can decrease immune function, but getting to and staying at a health body weight can restore immunity (29)!

Use the following information to get started on your road to better health with long-term weight management.

Know That It Won't Be Easy, But You Can Succeed 

The first thing to remember is that weight loss is not easy. Don't be hard on yourself if you've struggled with maintaining a healthy weight. This is a health concern for many people.

Health experts know that many, many people struggle with weight loss. Nobody finds it easy to make healthy food choices when confronted with fast food restaurants and vending machines! However, by changing the way you think about food and health and improving a few habits, you CAN succeed at weight loss.

• Consult with a Registered Dietitian (RD) or receive support from a weight loss organization such as Weight Watchers©. Either of these approaches will work to help you develop a sensible and successful weight loss plan. 
• Be sure you think about weight loss and healthy eating as a lifestyle rather than a temporary diet. This is important! For long-term weight loss success, you must change your eating and exercise habits permanently.
• For more information on this topic, please see our information on Tips for Reaching and Maintaining a Healthy Body Weight and More Information on Healthy Body Weight.

Find A Supportive Health Care Provider!

This is one of the most important things you can do to help yourself succeed. Research tells us that many health care providers have a very negative view of men and women who are overweight and obese (30).

When you want to lose weight and improve your health, the last thing you need is a health care provider who is critical and unsupportive!

• Talk to your doctor honestly about your desire to lose weight and improve your health.
• Tell him/her that you would like help with your goals.
• Ask for a referral to a weight loss specialist such as a Registered Dietitian.
• If your doctor is not supportive of your goals or places the focus on blaming you for being overweight, consider finding a more supportive health care provider.
• If your health care provider is not supportive of your goals, you will be less likely to make them a priority yourself.

Modify Your Views & Goals

One of the most important things you can do to increase your chances of success with weight loss is to view these changes as A GIFT!

• Losing weight to improve your health is NOT a punishment. It is a gift.
• Realize that weight loss won't be easy, but when you succeed, you will feel better, you will have a better quality of life, you will decrease your risk of many serious diseases, and you will live longer!
• This is a gift to you, but it is also a gift to your family and friends. Anyone who cares about you will benefit from the gift of health that YOU give yourself by maintaining a healthy body weight!
• Make your goal IMPROVED health, NOT 'looking better'. While improvements in appearance are a great benefit of weight loss, focusing on the HEALTH benefits of weight loss will help you meet your goals today and for the long-term!
• Health benefits include ANYTHING that will help motivate you. This can include sleeping better; having less joint & muscle pain; having more energy; lowering your risk of cancer, heart disease, high blood pressure, diabetes, stroke and other serious conditions; improving your sense of well being and self-image; and just about any other health improvement you can think of. Weight loss will help with all of these goals!!

Examine Your Risk

Look at your current height and weight and be honest with yourself about whether you are overweight or obese. This may be harder than it sounds!

Researchers have found that many overweight and obese adults do not know that they are above a healthy body weight and therefore at increased risk of many serious conditions and diseases (31-33).

This is the first step to managing weight and improving health, including reducing cancer risk! How do you know if you're overweight or obese? You can use a measure called Body Mass Index (BMI). BMI is a way to measure body weight, while taking into account a person's height. 

To determine your BMI, please see our Body Mass Index Calculator.

Eliminate High Calorie/Low Nutrition Foods

New research is telling us that certain parts of our diet might be contributing a lot to the problem of obesity. One potential obesity contributor is high fructose corn syrup. Studies tell us that the eating a lot of high fructose corn syrup may be making the obesity problem worse (34,35).

What is high fructose corn syrup?

High fructose corn syrup is a sweetener found in many commonly eaten foods and beverages. One of the biggest sources of high fructose corn syrup in our diets is soda pop. There are many other sources of high fructose corn syrup as well. To address this problem...

• DROP THE POP habit. Soda pop is nearly pure high fructose corn syrup. This includes both 'brown' and 'clear' regular soda pops.
• Let me say that again. DROP THE POP habit. Regular soda pop is nothing but PURE sugar, in particular, high fructose corn syrup. Worse yet, it is liquid, which means it affects your body more quickly than sugar in foods.
• When you switch from regular soda pop to water, decrease the amount of soda pop you drink slowly. This will help prevent symptoms of caffeine withdrawal, such as headaches.
• If you do not like plain water, try carbonated water that does not contain high fructose corn syrup. Look at the label. If the water contains calories, PUT IT BACK. Instead pick a brand that does not contain calories. Plain, flavored or carbonated water will not contain calories.
• Small amounts of diet sodas are ok, but they do not add anything of nutritional benefit to your diet. For this reason, think of a diet soda as a treat, not a daily necessity.
• Other sources of high fructose corn syrup include fruit punches (6 ounces of 100% fruit juice is ok to count as one serving of fruit per day); baked goods such as doughnuts, cookies, cakes, candy bars, hard candy, and other desserts; jams; jellies; sauces and dressings; and many other highly processed foods such as instant meals and snack foods.
• Become a label reader. This is the only way to limit the amount of high fructose corn in your diet. Even many of the breads we eat contain high fructose corn syrup!
• What are highly processed foods? Think of foods that are as close to their 'natural form' as possible, such as fresh vegetables and fruit. Now think of a more processed food, for example, a corn chip. A corn chip is made of corn, but it's NOT a whole food, it is highly processed! To make a corn chip, first the corn is picked, then ground and crushed. Next the fiber portion of the corn is thrown out. Then the corn is fried in processed fat (hydrogenated fat). Next it is treated with artificial flavors, dyes, and preservatives. This hardly looks like corn anymore!
• Now think of corn on the cob. It is picked, shipped, and ends up on your dinner table! It is not processed. It is a WHOLE food. The less processing that a food undergoes before you eat it, the better it is for you.
• Make dessert an OCCASSIONAL treat. There is nothing wrong with having a sweet treat now and then. Just make sure 'now and then' only means 2-3 times per week.

Watch Portion Sizes

• If you do eat in restaurants, watch your portion sizes! Instead of eating everything on your plate, try asking for a 'to go' box at the BEGINNING of your meal. Place a portion of the food into the 'to go' box and then enjoy the rest of your meal.
• When eating at home, try measuring your portion sizes for a while. For example, a serving of pasta is 1/2 cup cooked. Try measuring this out to see what it looks like. If you want more than one serving, this can be ok, just be sure you KNOW you are eating more than one serving. Sometimes, just being aware of what you are eating can help you make better choices.

Get Moving

Exercise is one of the most important ways to help yourself keep of weight for good. It is very hard to succeed with permanent weight loss if you don't exercise regularly (36). And at least one research study tells us that if you exercise along with moderate dieting when losing weight, the exercise will help to keep your immune system healthier as you lose weight (24)! In other words, people who only diet to lose weight have decreases in immune function, while people who diet AND exercise do not have these same decreases in immune function.

• Talk to your health care provider about a good exercise plan for you.
• Be sure you receive clearance from your doctor BEFORE beginning an exercise plan!!
• Exercise plans do not have to be fancy or very hard. Simply taking a long, brisk walk each day can be enough to aid with weight loss and make you healthier.
• Find an exercise buddy such as a family member or co-worker. It is harder to skip exercise when you plan to meet someone for it.
• Schedule exercise, even 10 minutes, into your day. Write it on your calendar. If you don't make time for it, you won't do it.

NOTE: If you are in cancer treatment, these diet changes may not be right for you.

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Publish Date: 10/2004