Long-Term Effects of Low-Carb Diets Like Keto and Paleo

Low-carb diets are often touted as the best way to lose weight. Indeed, short-term clinical trials show the effectiveness of switching from a standard western diet to a low-carb diet for weight loss.  However, there is more to this than meets the eye, not the least of which is emerging data regarding the long-term health effects of these type of diets.

Recently, details of new research on this topic were published.  A prospective cohort study examined the associations of LCDs (low-carb diets) and LFDs (low-fat diets) with health outcomes over a long follow-up timespan of 23 years.  Participants were collected from the database of the NIH-AARP (National Institutes of Health – American Association of Retired Persons) Diet and Health Study of Retired Persons, which began in 1995 and recorded detailed data from more than half a million middle-aged and older people in the United States.  Documented information includes physical activity, family medical history, cancer screening, body size and early life diet along with follow-up questionnaires on physical activity, medication use, health diagnoses, family history of cancer, diet and lifestyle. After excluding participants already suffering from cancer, heart disease, stroke, diabetes, end-stage kidney disease or overall poor health, over 371,000 participants remained to be included in this study.   Age range of participants was 61.2 years plus or minus 5.4 years.  Food intake was evaluated through a Diet History Questionnaire and validated during the study with 24-hour diet recalls.  (1)


Notes on How the Study Was Conducted (1)

Researchers calculated six different Diet Scores to which they allocated study participants as follows:

Overall LCD Score:  Adherence to a diet low in total carbohydrate, high in total fat and high in total protein.

Healthy LCD Score:  Adherence to a diet low in low-quality carbohydrate, high in unsaturated fat and high in plant protein.

Unhealthy LCD Score: Adherence to a diet low in high-quality carbohydrate, high in saturated fat and high in animal protein.

Overall LFD Score: Adherence to a diet low in total fat, high in total carbohydrate and high in total protein

Healthy LFD Score: Adherence to a diet low in saturated fat, high in high-quality carbohydrate and high in plant protein.

Unhealthy LFD Score: Adherence to a diet low in unsaturated fat, high in low-quality carbohydrate and high in animal protein.


For the purposes of this study, high-quality carbohydrates included carbohydrates from whole grains, whole fruits, legumes and non-starchy vegetables.  Low-quality carbohydrates included carbohydrates from refined grains, added sugar, fruit juice, and starchy vegetables.

The aim of this study was to examine the relationship of each Diet Score pattern with total mortality (death) and death from specific causes over the 23-year duration of this research.  The HEI-2015 Healthy Eating Index was also taken into account to reflect overall diet quality relative to the 2015-2020 Dietary Guidelines for Americans.

In addition, substitutions among macronutrients were carried out with resulting changes in mortality risk assessed.  For instance, scientists looked at the effect of replacing 3% of total energy intake from low-quality carbohydrates with 3% of total energy from high-quality carbohydrates, keeping fat and protein the same.

Deaths occurring during the first five years of follow-up were excluded to limit the effect of undiagnosed chronic diseases that may have been present in some participants at the start of the study.


Results (1)

Healthy LFDs (low intake of saturated fat and high intake of high-quality carbohydrates and plant protein) were associated with a reduction in death from all causes including cardiovascular disease and cancers by up to 34%.

Unhealthy LCDs were linked to an increased risk of mortality from any cause of up to 38%.

Overall LFDs and unhealthy LFDs were linked to a slight lowering of mortality risks.

Both overall LCDs and unhealthy LCDs were connected to significantly higher total mortality, mortality from cancer and mortality from cardiovascular disease.

Healthy LCDs with restricted intake of low-quality carbohydrate and higher consumption of unsaturated fat and plant protein, were linked to slightly lower total mortality.

Healthy LCDs low in total or high-quality carbohydrates increased the risk of death from all causes and cardiovascular disease.

Replacement of 3% of energy from either saturated fats or low-quality carbohydrates with plant protein was associated with 10% lower risk of mortality from all causes; 11% lower risk of mortality from cardiovascular diseases; and 5% lower risk of mortality from cancers.


Summing Up 


The conclusion of this study was the following:

Consuming a healthy low-fat diet (LFD) with minimal saturated fat intake

is the most effective way to eat for healthy aging among middle-aged and older adults. (1)



LCDs are associated with weight loss.  However, their use for long periods of time has not been extensively studied. Investigations delving into this aspect of LCDs are illuminating their destructive nature during sustained consumption, showing higher rates of death from all causes as well as death from cancers, peripheral artery disease and coronary artery disease. (2)  Meanwhile, whole food plant-based diets, which are an example of a healthy LFD (low in saturated fat and high in high-quality carbohydrates and plant protein) demonstrate even stronger correlations with losing weight.  And more compelling, a whole food plant-based diet also supports longevity and a healthy cardiovascular system and reduces the development of metabolic diseases such as type-2 diabetes.  It is becoming clear that the source, quality and composition of dietary carbohydrates all have significant influences on health-related outcomes including total and cause-specific mortality.  (1)

The BROAD Study from 2017 divided its 65 subjects, aged between 35 and 70 into two groups; one group, the control group, made no changes in their diets and received standard medical care, and the other group, the intervention group, received education and support to convert to a whole-food plant-based diet.  Each participant in the intervention group was given a ‘traffic-light’ diet chart outlining what to eat and what not to eat and they were encouraged to consume all the healthy foods that they wanted with no calorie counting or portion control.  The BROAD Study is an example of the “gold” standard” in research, a randomized controlled trial.  The randomization of subjects (deciding which group each participant is to be put into) was done by computer through random.org.  (2)

BROAD Study results are startling.  The whole food plant-based intervention group lost an average of 18 pounds after 3 months and 26 pounds after 6 months and this weight loss was sustained over 12 months.  Their cholesterol dropped on average by 16% and their LDL-cholesterol decreased by an average of 26% after 3 months.  Medication use was lowered by about 30%.  In addition, participants with type-2 diabetes experienced improvements in their disease with half of them discontinuing their diabetes medications and some no longer considered to be diabetic at all.  Contrast this with the control group who had only very modest weight loss and cholesterol lowering effects.  Their medication use did not only not decrease, it actually increased by about 8%.  Study researchers pointed out that the whole food plant-based diet in this trial had achieved greater weight loss at 6 and 12 months than any other trial published in the medical literature that does not limit food intake.  (2)

A study published in 2019 examined the link between LCDs and overall or cause-specific mortality from previous cohort studies.  Results indicated that people eating the lowest amount of carbohydrates had 32% higher risk of overall mortality; 50% greater risk of death from cardiovascular disease; 52% increased risk of death from cerebrovascular disease; and 36% greater risk of death from cancer.  Study authors suggested that further studies are needed to confirm these findings but they indicate that practitioners may need to rethink the recommendations for LCDs in weight loss. (3)

Here is the bottom line.  Though LCDs often have the loudest hype regarding their link to losing weight,  their long-term use is associated with poor health outcomes.  Moreover, LCDs are not the only way of eating that promotes loss of weight.  There is no point in taking off some unwanted pounds if, at the same time, you’re setting yourself up for the imminent development of chronic diseases like cardiovascular disease, cancer or diabetes.  Whole food plant-based diets have been proving themselves for decades not only as a healthy way to lose weight but also as a path towards a long and vigorous life.  They encourage a diet made up of foods that are rich in all the nutrients, both macronutrients and micronutrients, that are needed to support health and that avoids foods that are harmful to health.  (4)  With the added advantage to our environment that eating plant-based offers, the choice seems simple.




1  Zhao, Y, Li, Y, Wang, W, Song, Z, Zhuang, Z, Li, D, et al. Low-carbohydrate diets, low-fat diets, and mortality in middle-aged and older people: A prospective cohort study. J Intern Med. 2023; 00: 1– 13.

2  Wright, N., Wilson, L., Smith, M., Duncan, B., Mchugh, P. The BROAD study: A randomised controlled trial using a whole food plant-based diet in the community for obesity, ischaemic heart disease or diabetes. Nutr Diabetes. 2017;7(3):e256.

3  Mazidi, M., Katsiki, N., Mikhailidis, D.P., Sattar, N., Banach, M. Lower carbohydrate diets and all-cause and cause-specific mortality: a population-based cohort study and pooling of prospective studies. Eur Heart J. 2019 Sep 7;40(34):2870-2879. Doi: 10.1093/eurheartj/ehz174. PMID: 31004146.

4  https://www.healthline.com/health-news/how-switching-to-a-plant-based-diet-can-add-years-to-your-life-no-matter-what-age-you-are


Promoting a healthy adventurous lifestyle powered by plants and the strength of scientific evidence.

My name is Debra Harley (BScPhm) and I welcome you to my retirement project, this website. Over the course of a life many lessons are learned, altering deeply-rooted ideas and creating new passions.

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