The Duchess of Windsor famously said, “You can never be too rich or too thin.” Well, it seems maybe you can. . .

To stay healthy, one of the things you always hear about is to keep your weight in check. Obesity takes a heavy toll on joints, heart and lungs, liver and just about everything else in the body. It’s associated with cancer, cardiovascular disease, diabetes and dementia.

But being underweight, or losing a lot of weight in a short amount of time, comes with its own set of problems… especially for your brain.

People with intermediate and advanced stages of Alzheimer’s disease usually lose weight because they have difficulties eating, or if they don’t have consistent care they may not be eating on their own.

The new findings go a bit further. Researchers are now seeing evidence that a sudden weight loss in older people who have no symptoms of cognitive decline may be an early warning sign of the disease.

A 37-year study of body mass index (BMI) and dementia in women in Gothenburg, Sweden found a correlation between a decline in BMI or being underweight and a dementia diagnosis.1

During the study, published in 2012 in the Journal of Alzheimer’s Disease, researchers noted that women who developed dementia had a smaller increase in BMI from ages 38 to 70. After age 70 the dementia patients had a lower BMI than their healthy counterparts, leading the researchers to believe that BMI is a common risk factor from mid- to late life.

Another study showed that in a group of people between the ages of 65 and 95, the ones who developed dementia of the Alzheimer type (DAT) lost twice as much weight in the year prior to diagnosis compared to the participants who did not develop dementia (1.2 pounds vs. 0.6 pound).2

Researchers concluded that weight loss may be a preclinical indicator of Alzheimer’s disease. I have to say the difference in weight between the two groups is so small it seems rather insignificant, but let’s roll with it and see if we can learn anything. . .

What’s the Connection?

Although reasons for sudden weight loss can vary, there are theories about why it might contribute to dementia.

One is that the brain simply isn’t getting the essential micronutrients, fatty acids and vitamins it needs to stay robust. Without these basic building blocks of brain tissue, the brain can’t fight off inflammation and oxidative damage, leading to decay and cognitive impairment.3

Sudden weight loss may also indicate the early onset of a completely different condition that, if left untreated, could increase a person’s risk for developing dementia.

The triggering conditions include depression, viral infections, dental problems, side effects brought on by medication, excess alcohol use or cancer.

If you notice change in a loved one’s eating habits — maybe they’re not eating as much as they used to or they’re living off junk food — don’t ignore it. Boosting nutrition with whole foods or supplements may help to keep the brain healthy enough to avoid developing Alzheimer’s disease.

“Too Thin” is Not a Problem for Most of Us!

My fear here is that people who need to lose weight might rationalize that they’re just fine the way they are. Don’t kid yourself. The findings I just discussed are limited and very tentative. They’re nothing compared to the massive evidence that obesity does great harm.

Being overweight is an epidemic that we know is killing millions of people prematurely. Meanwhile, there’s a ton of evidence that being ten percent underweight adds years to life, even decades. (Admittedly, starving myself skinny is beyond my willpower – my weight is healthy but not Duchess-of-Windsor thin.)

Controlled, intentional weight loss is actually good for your cognition, as long as you’re getting enough nutrients to feed your brain and organs.

A 2015 study published in The Journal of Clinical Endocrinology & Metabolism evaluated the effects of calorie restriction, weight loss and cognitive functioning on 80 obese patients aged 60 or older who already showed signs of mild cognitive impairment (MCI).

The researchers followed the group for 12 months. At the end of that time, tests revealed that a lower BMI correlated with improvements in verbal memory, verbal fluency, executive function and global cognition.4

In an interesting side note, the patients who also had the APOE gene — associated with an increased risk of Alzheimer’s disease — showed the strongest association between reduced BMI and improvement on executive function tests.

If you’re overweight and have tried fad diets or have been prone to yo-yo dieting in the past, try working with a registered dietician, nutritionist or naturopath to help you lose the weight in a way you can stick to for the rest of your life, without feeling deprived.

Much of the value these people provide is motivation and coaching. They offer the extra push, the outside monitoring, that many of us need to make up for our own willpower deficit.


  1. 37 years of body mass index and dementia: Observations from the Prospective Population Study of Women in Gothenburg, Sweden.
  2. Accelerated weight loss may precede diagnosis in Alzheimer disease.
  3. Weight loss and Alzheimer’s disease: Temporal and aetiologic connections.
  4. Cognitive effects of intentional weight loss in elderly obese individuals with mild cognitive impairment.

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