Weight loss may reduce cancer risk, but beware of fad diets

Good nutrition and a healthy weight may help cancer patients better tolerate treatments and reduce the risk of a recurrence. Losing weight may also reduce the risk of many cancers that have been linked to obesity.

Like baseball and apple pie, dieting is one of the more popular American pastimes. One in six Americans report being on a special diet to lose weight or to manage a chronic health condition such as heart disease or diabetes.

Weight management and healthy eating also are critical tools for cancer patients. Good nutrition and a healthy weight help support the immune system and may help better tolerate treatments and reduce the risk of a cancer recurrence. For those who are overweight, losing excess pounds may reduce their risk of many cancers that have been linked to obesity.

Over the decades, fad diets have come and gone like fashion trends and hair styles. In the 1970s, there was the grapefruit diet—eating a grapefruit at every meal to burn more fat. In the 1980s, Oprah Winfrey’s 67-pound weight loss sparked the meal replacement shake craze. The ’90s heralded the low-carb, high-fat, high-protein Atkins® diet. Current diet trends include intermittent fasting, which involves varying schedules of eating and fasting during specific times of day or days of the week.

While fad diets have fattened the weight loss industry’s profits—a record $78 billion in 2019, according to marketresearch.com—they don’t seem to have made Americans thinner. The U.S. Centers for Disease Control and Prevention (CDC) reports that 42.5 percent of Americans 20 and older are classified as obese, while 74 percent are considered overweight or obese, the highest ever recorded. These figures represent a 26 percent increase since 2008.

Cancer patients and those in survivorship often have unique nutritional needs, potentially adding to challenges in managing their weight. Certain treatments may result in weight loss or gain and/or reduced energy levels, or they may necessitate temporary or permanent diet and/or exercise modifications. Achieving and maintaining a healthy weight are also important steps in helping to reduce cancer risk.

The obesity epidemic may also be fueling new cancer cases. Obesity is a known risk factor for several cancers, including postmenopausal breast cancer and reproductive cancers in women and cancers of the digestive system. Obesity and diabetes often go hand-in-hand, adding yet another cancer risk factor for many Americans.  

But it’s important for patients, or those in survivorship, to be aware of the health-related pitfalls of some diet plans. Others, who are obese or overweight and want to improve their overall health and reduce their risk of diseases, such as cancer, may find that fad diets produce short-term results, but fall short of helping to achieve long-term weight loss.

In this article, dietitian and oncology nutrition specialist Carolyn Lammersfeld, MBA, MS, RD, CSO, LD, Vice President of Integrative Care Services for Cancer Treatment Centers of America® (CTCA), offers cancer patients insight into some current dieting trends and shares key principles for dropping excess pounds and maintaining a healthy weight. Among topics she addresses are:

Nutritional support is one of many supportive care services offered to cancer patients at CTCA®. To learn more about integrative care services and how they can be used to help patients manage cancer-related side effects and improve their quality of life, call us or chat online with a member of our team.


The obesity epidemic and cancer risk

The American Society for Clinical Oncology predicts that if current trends continue, obesity will lead to more than 500,000 additional cancer diagnoses by 2030 in the United States alone.

In fact, obesity is overtaking smoking as the number one lifestyle risk factor for cancer, Lammersfeld says. “It used to be thought that adipose tissue or fat cells were inactive, but we’re learning that it may function more like an organ, where it may result in higher levels of hormones like postmenopausal  estrogen,” she says. "We know that people who are obese or carrying extra weight may have poorer wound healing and greater risk of infections after surgery, which increases the risk of poor outcomes.”

The American Cancer Society (ACS) warns that excess body weight increases the risk for many cancers, including:

Carrying extra weight may also trigger conditions that may increase cancer risk, including chronic inflammation, increased production of insulin, estrogen and other hormones, and immune suppression. Preclinical Research also indicates that fat cells may complicate cancer treatment by reducing the effectiveness of some chemotherapy drugs.

Lammersfeld’s advice

Weight management is more complicated than just what we put in our mouths. “Eating has emotional and social components, so having help with stress management, behavior modification and social support are important components to healthy eating,” she says.

“At CTCA, we have registered dietitians who can test resting energy expenditure (calorie needs) and body composition, and they understand individuals’ lifestyle and clinical needs during treatment and into survivorship,” she adds. “We personalize diet and nutrition advice, and counsel and coach our patients. For those who are not our patients or are awaiting care, we partner with organizations that can help with nutrition services and products, fitness and emotional health."

The pitfalls of fad diets

Fad diets are notorious for weight gain once the dieter stops following the plan. Dieting is difficult, and unless there’s a plan in place to address backsliding and regaining, the dieter is likely to put the weight back on within a couple years, and add even more pounds within five years, Lammersfeld says.

“Many times, there’s an all-or-nothing approach, and it’s very difficult for most people to stay on a diet long-term,” she says. Even if a person is losing weight, some diets may create other health issues.

“If a diet is really restrictive, bone health may be impacted by the lack of sufficient nutrients,” Lammersfeld says. “Are you losing muscle? Impacting immune health? Organs, like the heart, can be impacted. There’s some literature that shows that yo-yo dieting can have more negative impacts on health compared to just maintaining one’s weight and working on diet quality and physical activity. Depending on the type of diet, you may lose weight, but instead of losing adipose tissue (fat), you may lose muscle, and when you regain the weight, you gain even more fat. In the long run, you’re actually worsening your body composition.”

Jasmyn Walker, Clinical Oncology Dietitian at CTCA Phoenix, says there’s no single magic bullet when it comes to weight management. Instead, she recommends adopting a lifestyle that’s sustainable to improve specific conditions and overall health.

“At CTCA, we take specific components of nutrition and tailor plans for each patient’s comorbidities, symptoms, treatment plan and long-term goals,” she says. “Without appropriate guidance and direction, patients may do more harm than good.”

Ketogenic, Atkins and paleo

While these three low-carbohydrate, high-fat diets are not exactly the same, each calls for very few carbs, which contradicts the recommendations  the U.S. Department of Agriculture (USDA) and Department of Health and Human Services’ Dietary Guidelines for Americans. Those guidelines recommend adults get:

  • 45 percent to 65 percent of calories from carbohydrates
  • 20 percent to 35 percent from fat
  • 10 percent to 35 percent from protein

In comparison, keto, Atkins and paleo diets recommend between 60 percent to 90 percent of calories from fat.


The idea of the ketogenic (keto) diet is for the body to experience ketosis, a metabolic state in which fat, rather than carbs, is burned for energy. To enter ketosis, the daily intake of carbs must be below 50 grams, over several days, an amount significantly below the Dietary Guidelines for Americans, which recommends a daily carbohydrate intake of between 225 grams and 325 grams.


Paleo dieters are supposed to eat like our hunter-gatherer Paleolithic ancestors. This diet incorporates lean meats, fish, fruits, vegetables, nuts and seeds, while eliminating grains, dairy and processed foods.


The Atkins diet endorses limitless amounts of high-fat foods such as red meat, butter, cheese and bacon, and forgoing carbohydrates. It also calls for a daily carbohydrate intake of between 20 grams and 80 grams, though it focuses on net carbs, which is calculated by subtracting grams of fiber and sugar alcohols from the total number of carbs. The difference is what Atkins calls net carbs.

Lammersfeld’s advice

Some literature suggests that getting no more than 35 percent of calories from carbs may help with weight loss over a six-month period, but not for the long term compared with other approaches. Research is lacking on the long-term impact on heart health beyond a year.

At CTCA, we encourage patients to get their fat from healthier sources—avocado, nuts and seeds instead of dairy fat, processed meats and red meats. Stay within the guidelines of the American Institute for Cancer Research (AICR) or the American Cancer Society, both of which suggest relying on more plant-based foods, which generally have complex carbs, and limit red and processed meats.



Drinking your fresh fruits and veggies sounds easy enough, and it’s better than not consuming fruits or veggies at all, but this plan has its drawbacks.

One medium-sized orange is considered a single serving, for example, but that translates to just 4 oz. of juice. Most people don’t drink just 4 oz., Lammersfeld says, so they instead tend to overindulge, unwittingly absorbing a significant amount of carbs. Carbs break down to sugar and may cause blood sugar to rise or fall rapidly. “We prefer that people eat whole fruits or vegetables,” she said. “There’s also not the same feeling of fullness from drinking that there is from eating.”

In addition, some juicers extract the most fibrous part of the fruit or vegetable, removing many of the phytochemicals that benefit our cells.

Lammersfeld’s advice

Be cognizant that juicing your fruits and vegetables may not be the nutritional equivalent to eating them. Juicing may remove lots of the fiber and may contain high amounts of natural sugars, which may cause spikes in blood-sugar levels. Juicing is acceptable if it’s the only way you’re going to consume fruits or vegetables, as long as portions are limited and the juice is served with a meal to slow blood sugar spikes. Juicing greens with small amounts of carrot or fruit to sweeten may result in less natural sugar being consumed.

Intermittent fasting

There’s some compelling literature about this in-vogue weight loss strategy, though more clinical research is needed, Lammersfeld says. “There does seem to be something there,” she adds. “All of us intermittent fast when we sleep, so even experimenting with extending that a little bit by eating later in the morning or stopping eating earlier in the evening may be beneficial. This approach is interesting to a lot of us because you don’t necessarily have to restrict anything else but the timing of eating.”

A 2019 article published in the Journal of Experimental & Clinical Cancer Research suggests there’s “abundant and convincing preclinical evidence” to show short-term fasting’s benefits, specifically that it may “decrease toxicity and simultaneously increase efficacy of a wide variety of chemotherapeutic agents.”  The research also suggests at that short-term fasting may enhance the effects of radiotherapy and certain cancer drugs. The article says that clinical studies indicate that this weight management plan also may offer “a promising strategy to enhance the efficacy and tolerability of chemotherapy. It appears safe as an adjunct to chemotherapy in humans, and it may reduce side effects and DNA damage in healthy cells in response to chemotherapy.” The study’s authors cautions that more research is needed to “firmly establish” this early data.

Lammersfeld’s advice

Try experimenting with extending the time between the fasting period and your next meal. Focus on plant-based foods when you’re eating. As always, speak to your care team before trying this or any other diet.

Nutritional support is one of several supportive care services offered to patients at CTCA. To learn more about our integrative care model, call us or chat online with a member of our team.