August 11, 2021

A Surprising Effect Of Dementia. Does It Cause Weight Loss?

Written by: Amanda Cheong, M.D.

You’ve probably heard about dementia before. You’re likely familiar with Alzheimer’s disease, which is responsible for as much as 80% of all cases of dementia.[1]


Without knowing anyone diagnosed with this disease, we have an image of it in our minds. It’s often a confused and frail elderly adult with snow-white hair. Perhaps a healthy amount of wrinkles as they ask the same question on repeat. Imagine them with skin that’s sagging just a bit from some lost elasticity of youth.


Parts of this picture we’ve conjured up could be dismissed as a normal part of aging. After all, most elderly adults undergo changes in body composition. Age replaces the heavier lean body mass with a larger body percentage of fat.[2] Less bulk and density in older persons tends to be expected.


But when the weight of an older individual tumbles faster than anticipated, perhaps things aren’t as we expected.


Cognitive decline and declining weight


Compared with older adults without Alzheimer’s, nearly half of those with the disease reported experiencing significant weight loss.[3] At the very least, these two entities are related.


More than related to each other, weight loss can predict progression into dementia. A study done in 2016 followed a group of older adults who already had mild cognitive impairment for 4 years. Through this time frame, they checked up on this group to find out who developed dementia and who did not. The researchers found that weight loss was linked to having a 3.2 fold increased risk of having Alzheimer’s dementia. Weight loss was also associated with dementia knocking at the door around 2 years earlier than those without.[4]


Of course, every person is expected to have some normal variation in weight. A little bit off the scale for a few weeks doesn’t necessarily confer an increased risk of dementia.


It’s a little bit different between males and females. The risk of Alzheimer’s disease is higher in men if their body mass index or BMI (a value derived from someone’s weight and height) decreases by 10-15% over the course of 4 years. So it really does require a large and steady decline before things get worrisome. However, the numbers look rather different for women. It takes only a decrease in BMI of greater than 5% over the course of 4 years for them to have an increased risk of Alzheimer’s dementia.[5]


Learning from all of these studies on the relationship and risk of weight loss and dementia, we have yet to answer the question ‘why’.


Current theories on weight loss and dementia


Spoiler alert: we don’t actually have a sure answer. These are just theories that have been proposed to understand this phenomenon better. Stronger evidence for these theories comes at the heels of more rigorous research in the field. So, continue looking out for these new studies.


Dementia is characterized by cognitive decline and problems in memory. In Alzheimer’s dementia, this is chiefly episodic memory. They would sometimes forget what they were doing just a few minutes ago. Trains of thought turn to water-- too hard to grasp and harder still to keep. One theory states that it affects their memory by making them forget to eat or refuse to eat. This snowballs over the course of four years and would lead to an overall decrease in caloric intake.[6]


The sense of smell in the elderly with Alzheimer’s disease is also significantly reduced.[7] A person’s sense of smell being so closely related to their sense of taste. Bland tasting food doesn’t exactly whip up a good appetite. Difficulty in swallowing foods, especially in the later stages of Alzheimer’s, can also contribute to eating less food and then possibly weight loss.[6]


Except those with Alzheimer’s disease don’t eat less compared to other older adults without the disease.


Yes, those with Alzheimer’s dementia generally have poorer nutritional status compared to older adults without the disease. However, their caloric intake didn’t differ significantly from other elderly individuals. They were even noted to consume more calories, chiefly in the form of carbohydrates, per weight.[8]


Perhaps, the problem is not in the things they’re eating but in the activities they do. Those with dementia can have some behaviour changes due to their memory problems. They might pace around more often, having forgotten what they were planning to do. They might engage in repetitive behaviours that waste energy.[6] Some studies have shown that those with dementia don’t engage in more daily activities than normal. However, they may not have noted all the small things that could potentially add up.[8]


If they don’t eat significantly less and they may not engage in more activities, maybe their bodies are expending more energy without engaging in work. It may sound confusing-- expending energy by just existing. But this is actually called basal metabolic rate or the amount of energy used while at rest. Some theorize that those with dementia have an increased basal metabolic rate of greater than 10% or hypermetabolism. This can theoretically cause weight loss. However, studies remain divided on this topic. Some studies showed greater metabolism in patients with dementia while others showed less, and still others showed no significant changes.[6]


Others theorize that some of the medications for dementia can contribute to weight loss. A type of medication given to those with Alzheimer’s dementia is called acetylcholinesterase inhibitors (AChEi). A mouthful, I know. They’re chiefly used to prevent the degradation of certain molecules that help nerve cells speak to each other. This helps buff up the declining nervous system. It can also provide the elderly person with a few more lucid years, though they cannot stop the progression of the disease.[6]


They also come with undesirable side effects such as dose-dependent nausea, vomiting, diarrhea, and even loss of appetite. Certainly a recipe for weight loss![6] However, following patients for a year on these medications shows that they didn’t cause weight loss. Yes, those who lost weight had more significant cognitive decline. But it didn’t matter if they took this particular medicine or a different kind. One that didn’t cause the same sort of nausea and vomiting. They even found that the medication can be protective.[9]


What can you do?


Just being more perceptive of an elderly adult’s change in weight is already a good start. When caregivers of Alzheimer’s disease patients participated in a nutrition education program, they saw a decrease in patients with significant weight loss. Together with this, those under the program also had a better cognitive function.[10]


The nutrition program walked the caregivers through the consequences of weight loss in dementia patients. It focused on how to enrich foods, increase protein intake, and replace food that the elderly individual refuses to eat. But it also tackled how to cope with behaviors like only eating small amounts of food or refusing to use utensils.[10]


You’ve probably heard about dementia before. This may or may not be the first time you’re hearing about its relation to weight loss. But in a disease with a lot of uncertainties and no specific cure, our knowledge is power. While we wait for more rigorous and robust research to explain to us why weight loss tumbles into cognitive decline, we continue to keep ourselves educated on what we can do to mitigate these symptoms.



  1. Emmady PD, Tadi P. Dementia. [Updated 2021 Jul 6]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2021 Jan-. Available from:
  2. St-Onge MP, Gallagher D. Body composition changes with aging: the cause or the result of alterations in metabolic rate and macronutrient oxidation?. Nutrition. 2010;26(2):152-155. doi:10.1016/j.nut.2009.07.004
  3. White H, Pieper C, Schmader K, Fillenbaum G. Weight change in Alzheimer's disease. J Am Geriatr Soc. 1996;44(3):265-272. doi:10.1111/j.1532-5415.1996.tb00912.x
  4. Cova I, Clerici F, Rossi A, Cucumo V, Ghiretti R, et al. (2016) Weight Loss Predicts Progression of Mild Cognitive Impairment to Alzheimer’s Disease. PLOS ONE 11(3): e0151710.
  5. Kang SY, Kim YJ, Jang W, Son KY, Park HS, Kim YS. Body mass index trajectories and the risk for Alzheimer's disease among older adults. Sci Rep. 2021;11(1):3087. Published 2021 Feb 4. doi:10.1038/s41598-021-82593-7
  6. Franx BAA, Arnoldussen IAC, Kiliaan AJ, Gustafson DR. Weight Loss in Patients with Dementia: Considering the Potential Impact of Pharmacotherapy. Drugs Aging. 2017;34(6):425-436. doi:10.1007/s40266-017-0462-x
  7. Jung HJ, Shin IS, Lee JE. Olfactory function in mild cognitive impairment and Alzheimer's disease: A meta-analysis. Laryngoscope. 2019;129(2):362-369. doi:10.1002/lary.27399
  8. Wang PN, Yang CL, Lin KN, Chen WT, Chwang LC, Liu HC. Weight loss, nutritional status and physical activity in patients with Alzheimer's disease. A controlled study. J Neurol. 2004;251(3):314-320. doi:10.1007/s00415-004-0316-4
  9. Gillette-Guyonnet S, Cortes F, Cantet C, Vellas B; REAL.FR Group. Long-term cholinergic treatment is not associated with greater risk of weight loss during Alzheimer's disease: data from the French REAL.FR cohort. J Nutr Health Aging. 2005;9(2):69-73.
  10. Rivière S, Gillette-Guyonnet S, Voisin T, et al. A nutritional education program could prevent weight loss and slow cognitive decline in Alzheimer's disease. J Nutr Health Aging. 2001;5(4):295-299.
Article written by Amanda Cheong, M.D.
Dr. Amanda Cheong spent her formative medical years within the walls of the Philippine General Hospital, a high-volume tertiary institution built to serve the underserved. After graduating with a degree in medicine, she went on to write, edit, and compile healthcare stories from the start of the COVID-19 pandemic for an online anthology. Currently, she is involved in medical research as well as volunteer telemedicine consults. She enjoys writing fiction on the side when she’s not tending to her plants and three pet turtles.

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