Keto sweeteners – the best and the worst
To the left, in the green zone, are very-low-carb sweeteners that have generally been shown to have little impact on weight gain, blood sugar, or insulin levels.1 To the right, in the red zone, are sweeteners to strictly avoid.
The numbers corresponding to each sweetener represent the estimated long-term impact each product may have on blood sugar and insulin levels as compared to the same amount of sweetness from white sugar.2 For the purposes of this scale, pure white sugar is defined as having a number of 100.
The question marks by products labeled as “zero” represent what is currently known about their impact on blood glucose and insulin response only. These products are relatively new and their full effect on obesity, diabetes, liver health, the gut microbiome and long-term risk for metabolic or cardiovascular disease is not yet known. More research is needed.3
Products that have numbers with asterisks reflect that these products contain some carbs, often fillers such as dextrose (glucose).
For example, a Splenda packet provides about the same sweetness as two teaspoons of sugar, which is 8 grams of sugar. The packet contains about 0.9 grams of carbohydrate as dextrose. That’s 0.9 / 8 = 0.11 times the effect of sugar, for an equal amount of sweetness. Pure dextrose has a number of 100, so Splenda gets a number of 100 x 0.11 = 11.
The asterisks by xylitol and maltitol reflect that these sweeteners cause a blood glucose and insulin response, although less than sugar does. The number compares that relative response, out of 100, to the equivalent sweetness of pure dextrose.
If you are trying to stay in ketosis, avoid the sweeteners in the middle and red zone. Primarily use stevia or erythritol if you need sweeteners – though their long-term health impacts are not yet fully known.
Beware: the sweetener snare
The sweeteners to the left above might only have small or even negligible direct effects on weight and blood-sugar levels. But that’s not the only concern.
Here’s the potential sweetener trap: eating sweet-tasting foods and drinks may promote the craving for more sweet-tasting treats. Cravings aren’t kicked to the curb, they’re coddled and kept.4
These low-carb sweeteners are typically added to foods that mimic or replace items that the keto diet eliminates — sugary soft drinks, cakes, cookies, muffins, pastries, ice cream, candy, energy bars, and more. Sweet treats may entice you into eating when not hungry, raising the risk that you’ll end up consuming more than you need.
They also keep you tied to old patterns of your former high-carb eating, such as giving yourself sweet rewards that might have contributed to weight gain and metabolic issues in the first place. They may slow or stall weight loss or even cause weight gain on the keto diet.5 They may also trigger a relapse to non-keto eating.
Even the zero-calorie sweeteners in diet soft drinks may possibly contribute to long-term weight gain and metabolic issues.6 All sweet tastes, whether real sugar or sugar substitutes, act upon the same sweet taste receptors of the tongue and trigger similar brain neural reward pathways that according to researchers, “perpetuate their intake,” so they can maintain sugar addictions and cravings.7
Moreover, zero-calorie sweeteners’ impacts on pregnant women, the developing fetus and young children are unknown and could be potentially risky for long-term metabolic health.8 More research is certainly needed.
All of these reasons are why we at Diet Doctor encourage people on a keto diet to ideally avoid all sweeteners, if possible.
We do understand, however, that many people feel they need a sweet treat every so often. For some, facing a future devoid of birthday cake and ice cream could remove some joy from their lives. An occasional sweet treat might sometimes make sustaining the keto diet much easier.
Fortunately, over time, the keto diet reduces cravings for sweet-tasting foods for most people. It gets easier to control or ignore cravings; the desire for sweets diminishes.9 Many then find that the natural sweet taste of wholesome foods emerge. Tastebuds can become more attuned to subtle and rewarding flavours. The desire and need for sweeteners ease.
Using sugar as a sweetener
Real sugar as a sweetener comes in many shapes and forms: white, brown, demerara, icing, confectionary, maple syrup, coconut sugar, date sugar, and more.
Real sugar is a double molecule of glucose (50%) and fructose (50%). That makes sugar 100% carbs, and all these sugars have the same negative impacts on weight gain, blood glucose, and insulin response.10
On a keto diet, sugar in all its forms should be avoided. It will derail your progress.
Note that many sweeteners – white or brown sugar, maple syrup, coconut sugar and dates – have a number of exactly 100. This is because these sweeteners are made of sugar. For the same amount of sweetness as white sugar, you’ll get pretty much an identical effect of these sweeteners on blood sugar, weight and insulin resistance.
Worse than sugar: pure fructose
What’s even worse than sugar? Fructose. That’s because it goes straight to the liver and may promote fatty liver, insulin resistance, central obesity, and unhealthy lipid profiles, especially when consumed in excessive amounts.11
Unlike pure sugar with its pairing of glucose and fructose, sources of fructose are much slower to raise blood sugar and are given a lower glycemic index (GI) rating.12 But don’t let that low GI rating fool you! Fructose may still do a lot of metabolic harm over the long term — perhaps even more than pure sugar.
Fructose sweeteners — high fructose corn syrup, fruit juice concentrate, honey, molasses, agave syrup — are labeled 100+ in our image because of their detrimental long-term impact. They could be called super sugars. Agave syrup is the worst of all, with the highest fructose content: more than 60%.13
While all sweeteners have potential for negative impacts, if sustaining your keto journey is helped by the consumption of sweets from time to time, here are the 3 choices that may do the least harm.
Option #1: Stevia
Stevia is derived from the leaves of the South American plant Stevia rebaudiana, which is part of the sunflower family. Indigenous peoples in Paraguay and Brazil used the intensely sweet leaves in teas, medicines and to chew as a treat, most often simply taking fresh leaves or drying the leaves for various uses.
Commercial use and marketing of the natural leaves is not permitted in the US. These days the active sweet compounds, called stevia glycosides, are extracted and refined in a multi-step industrial process to meet with US and European regulatory requirements. The FDA, while not approving the unrefined leaves, has designated the refined extract as “Generally Regarded as Safe (GRAS).”
- It has no calories and no carbs.
- It does not raise blood sugar or insulin levels.14
- It appears to be safe with a low potential for toxicity.15
- Stevia is very sweet — 200 to 350 times the sweetness of sugar — and a little goes a long way.
- While intensely sweet, it doesn’t taste like sugar.
- Many people find stevia has a bitter after taste.
- It is challenging to cook with to get similar results as sugar and cannot be simply swapped into existing recipes.
- There’s not enough long term data on stevia to discern its true impact on health of frequent users.16
Sweetness: 200-350 times sweeter than table sugar.
Products: Stevia can be purchased as a liquid, powdered or granulated. Note that granulated stevia, such as the product Stevia in the Raw, contains the sugar dextrose. Some granulated stevia products, like Truvia, also contain erythritol and fillers.
Option #2: Erythritol
Made from fermented corn or cornstarch, erythritol is a sugar alcohol that occurs naturally in small quantities in fruits and fungi like grapes, melons and mushrooms. It is only partially absorbed and digested by the intestinal tract, which can cause gastrointestinal discomfort in some people.
- It has zero calories and no carbs.
- It does not raise blood sugar or insulin levels.17
- Its active compound passes into the urine without being used by the body.18
- In its granulated form it is easy to use to replace real sugar in recipes.
- It may prevent dental plaque and cavities compared to other sweeteners.19
- It doesn’t have the same mouthfeel as sugar – it has a cooling sensation on the tongue.
- It can cause bloating, gas and diarrhea in some people (though not as much as other sugar alcohols).
- Absorbing erythritol and then excreting it via the kidneys could potentially have negative health consequences (none are known at this time).
Sweetness: About 70% as sweet as table sugar.
Option #3: Monk fruit
While it’s derived from a round, green fruit that’s been grown for centuries in Southeast Asia, monk fruit is a relatively new sugar substitute on the market. Also called luo han guo, monk fruit was generally dried and used in herbal teas, soups and broths in Asian medicine. It was cultivated by monks in Northern Thailand and Southern China, hence its more popular name.
Although the fruit in whole form contains fructose and sucrose, monk fruit’s intense sweetness – about 200 times as strong as sugar – is provided by non-caloric compounds called mogrosides, which can replace sugar. In 1995, Proctor & Gamble patented a method of solvent extraction of the mogrosides from monk fruit.
While the US FDA has not ruled on monk fruit as GRAS (generally regarded as safe) it has publicly noted that it accepts manufacturers’ GRAS determination. In the last few years more than 500 monk fruit products have come to market in the US. Monk fruit has not yet been accepted for sale by the European Union, but approval appears to be pending.
- It does not raise blood sugar or insulin levels.20
- It has a better taste profile than stevia. In fact, it is often mixed with stevia to reduce cost and blunt stevia’s aftertaste.
- It is also mixed with erythritol to reduce expense and improve use in cooking.
- It doesn’t cause digestive upset.
- It is expensive.
- It is often mixed with other “fillers” like inulin, prebiotic fibres and other undeclared ingredients.
- Be careful of labels that say “propriety blend” as it may have little active mogroside ingredients.
Sweetness: 150-200 times as sweet as sugar.
Products: Granulated blends with erythritol or stevia, pure liquid drops, or liquid drops with stevia; also used in replacement products like monkfruit-sweetened artificial maple syrup and chocolate syrup.
Low carb: xylitol
If you chew sugar-free gum, you are usually chewing xylitol. It is the most common-sugar-free sweetener in commercial gums and mouthwashes.
Like erythritol, xylitol is a sugar alcohol derived from plants. It is produced commercially from the fibrous, woody parts of corn cobs or birch trees through a multi-step chemical extraction process. The result is a granular crystal that tastes like sugar, but is not sugar.
Xylitol is low carb, but not zero carb. Xylitol’s carbs can quickly add up on a keto diet, so it’s not a great option.
- Xylitol has a low glycemic index of 13, and only about 50% is absorbed in your small intestine.21
- When used in small amounts, it has a minor impact on blood sugar and insulin levels.22
- It has about half the calories, but the same taste as sugar.
- It can replace sugar 1 for 1 in recipes.
- It’s been shown to help prevent cavities when chewed in gum.23
- It can cause significant digestive upset (gas, bloating, diarrhea) even when consumed in small amounts.24
- It is highly toxic to dogs and other pets – even a small bite of a product made with xylitol can be fatal to dogs.25
Sweetness: Equivalent in sweetness to table sugar.
The following sweeteners are quite new and aren’t widely available at this time. Moreover, very little is known about their long-term impacts on health because there isn’t much research on them.
Inulin is a member of the fructans family, which includes a fiber known as fructo-oligosaccharides (FOS). As a fiber, it provides no digestible carbs and isn’t absorbed from the digestive tract. Although it’s found in some vegetables like onions and Jerusalem artichokes, chicory is the main source of inulin used in low-carb sweeteners and products.
Because inulin is rapidly fermented by gut bacteria, it can cause gas, diarrhea, and other unpleasant digestive symptoms, especially at higher intakes.26 Indeed, many people have reported these symptoms after consuming inulin-based sweeteners. However, inulin appears to be safe when consumed in small amounts.
Sweetness: 70-80% of the sweetness of sugar
In 2015, allulose was approved as a low-calorie sweetener for sale to the public. It’s classified as a “rare sugar” because it occurs naturally in only a few foods, such as wheat, raisins, and figs.
Although it has a molecular structure almost identical to fructose, the body isn’t able to metabolize allulose. Instead, nearly all of it passes into the urine without being absorbed, thereby contributing negligible carbs and calories.27
Some studies in animals suggest there may be health benefits to consuming allulose, but human research has been mixed.28 It reportedly tastes like sugar and doesn’t seem to cause digestive side effects when consumed in small amounts. However, large doses may cause diarrhea, abdominal pain, and nausea.´´29
Additionally, it is much more expensive than other sweeteners and isn’t widely available. Allulose has received GRAS (Generally Regarded as Safe) status from the FDA.
Sweetness: 70% of the sweetness of table sugar
Yakon syrup comes from the root of the yacón plant native to South America. It is a truly “natural” sweetener, similar to maple syrup. However, like inulin, yakon syrup contains fructo-oligosaccharides, which can cause digestive discomfort.
It has a lower glycemic index (GI) than most other sugars because a portion of the syrup is fiber. Still, one tablespoon of yakon syrup contains some digestible carbs (sugar). The exact amount can vary, but some estimates put it at around 9 to 13 grams of carbs per 100 grams of yacon root.30 Because yakon syrup is much more concentrated, however, you’ll get this same amount of carbs in about 2 tablespoons of yakon syrup.
Sweetness: About 75% as sweet as sugar.
BochaSweet is one of the newest sweeteners on the market. It’s made from an extract of the kabocha, a pumpkin-like squash from Japan. This extract reportedly has the same taste as white sugar, yet because of its chemical structure, it supposedly isn’t absorbed and contributes no calories or carbs.
Unfortunately, although it has received great reviews online, very little is known is about its health effects because there are few, if any, published studies on kabocha extract.
Sweetness: 100% of the sweetness of table sugar.
Beware: deceptive sweeteners
Do you know that some products with labels that identify them as “zero-calorie” sweeteners are almost 100% carbs?
Beware of Stevia in the Raw, Equal, Sweet’n Low and Splenda packets. They are labeled “zero calories” but they are not.
The FDA allows products with less than 1 gram of carbs and less than 4 calories per serving to be labeled “zero calories”. So manufacturers cleverly package about 0.9 grams of pure carbs (glucose/dextrose) mixed with a small dose of a more powerful artificial sweetener.
The labels reel in the consumer and satisfy the authorities. But the packages in fact contain almost 4 calories each, and almost a gram of carbs. On a keto diet that can quickly add up. Don’t be conned; don’t consume.
Almost as bad as sugar: maltitol
Maltitol is another sugar alcohol. It is made from the hydrogenation of the corn-syrup by-product maltose. It behaves in cooking and production very much like pure sugar so it is very popular in commercial “sugar free” products, such as candy, desserts, and low-carb products. It is also less expensive for food producers to use than erythritol, xylitol, and other sugar alcohols.
Do not consume maltitol on a keto diet. It has been shown to raise blood sugar and increase insulin response.32 It is not good for anyone with diabetes or pre-diabetes. It also has three-quarters of the calories as sugar.33
It is also a powerful laxative. While 50% of it is absorbed in the small intestine, the remaining 50% ferments in the colon. Studies have shown that maltitol may cause significant gastrointestinal symptoms (gas, bloating, diarrhea, etc.) especially when consumed frequently or in large amounts.34
Diet soft drinks on keto?
Can you drink diet soft drinks on a keto diet? We recommend you avoid them. Drink water, sparkling water, tea, or coffee instead.
As noted at the start of this guide, regular consumption of sweet substances, even with no calories, will maintain cravings for sweet tastes. Your palate will remain tied to sweet flavours and be less likely to learn to enjoy the natural, flavourful but less intense sweetness of keto foods.
Other health concerns are suspected, but unproven, with many of the artificial sweeteners used, like aspartame, acesulfame K and sucralose.37
If you must drink diet sodas, however, you will likely still stay in ketosis. Regular soda, sweetened with sugar or high fructose corn syrup, will kick you right out of ketosis. Do not consume.
A final word on keto sweeteners
Yes, it’s pretty clear, we’re not a fan of sweeteners. While some sweeteners may be better than others, the best strategy for achieving optimal health and weight loss may be learning to enjoy real foods in their unsweetened state.
A 2016 study found many of the positive research on sugar substitutes are funded by industry and full of conflict of interest, research bias and unreproduced findings.38
It might take a little time for your taste buds to adapt, but over time, you may discover a whole new appreciation for the subtle sweetness of natural, unprocessed foods.
Can’t imagine living without sweet foods? If you try, do you find it almost impossible to curb the cravings? Do you find yourself then binging on sweets? You might be interested in our course on sugar addiction and how to take back control. And yes, you can do it!
A large review of 46 trials found that aspartame, saccharin, stevia, and sucralose had minimal to no effect on blood sugar and insulin response:
A controlled study in lean and obese adults found that erythritol had little to no effect on blood sugar and insulin levels:
American Journal of Physiology, Endocrinology & Metabolism 2016: Gut hormone secretion, gastric emptying, and glycemic responses to erythritol and xylitol in lean and obese subjects [crossover trial; moderate evidence] ↩
As described below in more detail and with references, the fructose in sugar results in a slower blood sugar and insulin response compared to glucose.
However, there are signs that the long-term effects of fructose could still be more problematic from a health and weight perspective, due to its negative impacts on liver health and insulin resistance when consumed in large amounts.
As this might result in higher glucose and insulin levels in the long term, sweeteners that are higher in fructose than regular sugar are marked with a 100+, compared to 100 for regular sugar. ↩
Here are three recent reviews making this point:
Canadian Medical Association Journal 2017: Nonnutritive sweeteners and cardiometabolic health: a systematic review and meta-analysis of randomized controlled trials and prospective cohort studies [systematic review; moderate evidence]
Research suggests that these sweeteners partially activate the “food reward” pathway responsible for cravings:
Observational studies have shown a link between frequent artificial sweetener use and weight gain:
One study found that people assigned to drink only water for 12 weeks lost more weight and had less insulin resistance than people who drank diet sodas for 12 weeks – even though both groups followed the same weight-loss plan.
American Journal of Clinical Nutrition 2015: Effects on weight loss in adults of replacing diet beverages with water during a hypoenergetic diet: a randomized, 24-wk clinical trial [moderate evidence]
Physiology & Behavior 2016: Recent studies of the effects of sugars on brain systems involved in energy balance and reward; relevance to low calorie sweeteners [overview article; ungraded evidence] ↩
Nutrients 2018: Early-life exposure to non-nutritive sweeteners and the developmental origins of childhood obesity: global evidence from human and rodent studies [overview article; ungraded evidence] ↩
In a small study, most people who cut out all sugar and artificial sweeteners from their diet reported that their sugar cravings stopped after 6 days.
Sugar is sugar. And even small to moderate amounts – especially when consumed in beverage form – can promote inflammation and have negative effects on blood sugar and triglyceride levels:
American Journal of Clinical Nutrition 2011: Low to moderate sugar-sweetened beverage consumption impairs glucose and lipid metabolism and promotes inflammation in healthy young men: a randomized controlled trial [moderate evidence]
Journal of Nutrition 2015: Consumption of honey, sucrose, and high-fructose corn syrup produces similar metabolic effects in glucose-tolerant and -intolerant individuals [randomized crossover trial; moderate evidence]
Studies in overweight and obese adults who consumed high-fructose beverages for 10 weeks gained weight and experienced a worsening of insulin resistance and heart disease risk factors:
The Journal of Clinical Investigation 2009: Consuming fructose-sweetened, not glucose-sweetened, beverages increases visceral adiposity and lipids and decreases insulin sensitivity in overweight/obese humans [randomized controlled trial; moderate evidence]
European Journal of Clinical Nutrition 2012: Consumption of fructose-sweetened beverages for 10 weeks reduces net fat oxidation and energy expenditure in overweight/obese men and women [randomized controlled trial; moderate evidence]
Some, although not all, reviews on dietary fructose conclude that consuming it on a regular basis may lead to metabolic health issues:
GI = glycemic index, a measure of how quickly a carbohydrate-containing food results in a blood sugar increase after eating it. ↩
This has been shown in studies of both lean and obese adults:
International Journal of Obesity 2017: Effects of aspartame-, monk fruit-, stevia- and sucrose-sweetened beverages on postprandial glucose, insulin and energy intake [randomized controlled trial; moderate evidence]
Appetite 2010: Effects of stevia, aspartame, and sucrose on food intake, satiety, and postprandial glucose and insulin levels [randomized controlled trial; moderate evidence] ↩
Obesity (Silver Spring) 2018: Non-nutritive sweeteners in weight management and chronic disease: a review [overview article; ungraded evidence]At least one study shows that large amounts of stevia may increase insulin secretion and might still drive fat storage and metabolic issues:Metabolism 2004: Antihyperglycemic effects of stevioside in type 2 diabetic subjects [randomized controlled trial; moderate evidence]
American Journal of Physiology, Endocrinology & Metabolism 2016: Gut hormone secretion, gastric emptying, and glycemic responses to erythritol and xylitol in lean and obese subjects [randomized controlled trial; moderate evidence] ↩
Journal of Obesity 2017: Effects of aspartame-, monk fruit-, stevia- and sucrose-sweetened beverages on postprandial glucose, insulin and energy intake [randomized controlled trial; moderate evidence]
European Journal of Clinical Nutrition 2017: Effects of non-nutritive (artificial vs natural) sweeteners on 24-h glucose profiles [randomized controlled trial; moderate evidence] ↩
American Journal of Physiology, Endocrinology & Metabolism 2016: Gut hormone secretion, gastric emptying, and glycemic responses to erythritol and xylitol in lean and obese subjects [randomized controlled trial; moderate evidence] ↩
Although this is presumably related to xylitol being partially fermented in the colon, some early research suggests that xylitol might potentially also lead to adverse changes in gut bacteria:
Although individual tolerance may vary, even small doses of inulin (5-10 grams) have been found to slightly increase digestive symptoms like gas and bloating:
For instance, a recent study found no evidence that allulose improved blood glucose response in healthy people:
Nutrients 2018: A double-blind, randomized controlled, acute feeding equivalence trial of small, catalytic doses of fructose and allulose on postprandial blood glucose metabolism in healthy participants: the fructose and allulose catalytic effects (FACE) trial [moderate evidence]
However, a similar study conducted the same year found that allulose did improve blood glucose response when consumed by people with type 2 diabetes:
Diabetes, Obesity, and Metabolism 2018: The effect of small doses of fructose and allulose on postprandial glucose metabolism in type 2 diabetes: a double-blind, randomized, controlled, acute feeding, equivalence trial [moderate evidence]
These concerns are mainly based on the results of animal experiments conducted over many years:
Maltitol has the highest glycemic index (35) and insulin index (27) of all sugar the alcohols, and a large portion is absorbed into the bloodstream:
Maltitol provides about 3 calories per gram, compared to 4 calories per gram provided by sugar:
European Journal of Clinical Nutrition 1994: Digestion and absorption of sorbitol, maltitol and isomalt from the small bowel: a study in ileostomy subjects [randomized controlled trial; moderate evidence]
Gastroentérologie Clinique et Biologique 1991: Clinical tolerance, intestinal absorption, and energy value of four sugar alcohols taken on an empty stomach [randomized controlled trial; moderate evidence] ↩
European Journal of Clinical Nutrition 1996: Dose-related gastrointestinal response to the ingestion of either isomalt, lactitol or maltitol in milk chocolate [randomized controlled trial; moderate evidence]
In a study of overweight women who regularly consumed diet soda, those in the group who replaced their diet drinks with water lost 2.6 pounds (1.2 kg) more than the women who continued drinking diet soda even though both groups followed the same weight-loss program:
The American Journal of Clinical Nutrition 2015: Effects on weight loss in adults of replacing diet beverages with water during a hypoenergetic diet: a randomized, 24-wk clinical trial [moderate evidence]
International Journal of Obesity 1997: The effect of sucrose- and aspartame sweetened drinks on energy intake, hunger and food choice of female, moderately restrained eaters [non-controlled study; weak evidence]
Observational studies have shown an association between routine use of artificial sweeteners and an increased risk of weight gain, diabetes, and heart disease:
Canadian Medical Association Journal 2017: Nonnutritive sweeteners and cardiometabolic health: a systematic review and meta-analysis of randomized controlled trials and prospective cohort studies [systematic review of randomized controlled trials and cohort studies; moderate evidence]
- New research: could non-caloric sweeteners cause weight gain?
- How artificial sweeteners could make us eat more
- Diet Pepsi may cause cancer – consumer watchdog downgrades it from “caution” to “avoid”
PLoS One 2016: Relationship between research outcomes and risk of bias, study sponsorship, and author financial conflicts of interest in reviews of the effects of artificially sweetened beverages on weight outcomes: a systematic review of reviews [strong evidence] ↩