No evidence that low GI is better than high GI for weight loss & obesity management

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Eddy Edson

Eddy Edson

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Relationship to Diabetes
Type 2

Metastudy published last November.

nmab093fig1.jpg


Sod-all difference, and sometimes higher GI associated with lower BMI.

In general:

In view of all the contrary evidence from observational cohort studies and meta-analyses of RCTs, it is surprising that the hypothesis that low-GI (“slow-carb”) diets are superior for weight loss and obesity prevention persists. Carbohydrate quality, including GI, clearly impacts many health outcomes (17, 18, 25), and several meta-analyses have reported higher risks of T2D, cardiovascular disease, and stroke associated with high-GI diets (25, 86–89). However, GI as a measure of carbohydrate quality appears to be unimportant as a determinant of BMI or diet-induced weight loss. We contend that GI is an imprecise measure of the glycemic response of a food when applied to foods in a meal, and that the GI assigned to foods from an FFQ may differ significantly from actual GI. Nutrient density, dietary fiber and whole-grain content of carbohydrates, and percentage of added sugar, are more important qualities (17, 18, 78). Further, a focus on staple carbohydrate foods and the positive nutrients they contribute to diet quality as compared with the detractor nutrients associated with indulgent foods is important in characterizing the quality of carbohydrates. As for body weight and obesity, there is scant scientific evidence that low-GI diets are superior to high-GI diets for weight loss and obesity prevention.
 
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Couldn't get the link to work

I thought GI was all about blood glucose stuff not BMI or weight control. Can anyone explain the link between them?
 
The data around GI seemed pretty unconvincing for BG management when the 2015 NICE T1 guidelines were in development too if memory serves too.

I’m not sure, but maybe the sampling and methodology just isn’t robust enough. Getting an average value from 100 people eating 50g in carbs of one single thing, just doesn’t fully reflect the complexity of mixed meals, and the individual variation of gut biome, metabolism, genetic components etc. Many folks on the forum have found that the common suggestion from DNs to switch to brown versions of carbs is unlikely to help all that much.

But at the same time, I don’t think it’s completely useless at an individual level either - because some of the indications (at least from a BG perspective) may be helpful if you haven’t got the opportunity to check your own individual response to things.

Where scientific studies have to isolate the action and confound for variables to see whether or not this one thing ‘works’, I think it can miss the interactions and ‘more than the sum of its parts’ effect that can happen when things combine (or compete)?
 
Gwynn said:
Couldn't get the link to work

I thought GI was all about blood glucose stuff not BMI or weight control. Can anyone explain the link between them?
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Sorry, fixed link.

The high-GI-causes-weight-gain story is part of the carbs-are-evil story.

More precisely, it ties in with the "Carbohydrate Insulin Model" of weight gain/obesity, which goes something like: carbs => insulin production => fat gets stored rather than burned, or some variation on that. The higher the GI, the more pronounced the effect. Or so the story goes.

This whole "CIM" has been progressively refuted over the last several years, and this metastudy is part of that. From the intro:

The glycemic index (GI) was introduced in 1981 as a means to classify foods according to their effects on postprandial blood glucose (1). Since then, >10,000 scientific articles have been published on GI (PubMed search May 2021), and several popular books have extolled the purported health benefits of low-GI diets (2–4), including better weight control and reduced obesity risk (5, 6). High-GI foods are frequently referred to as “fast carbs.” A May 2021 Google search for “fast carbs” produced >47,000 results, many of which featured websites that portrayed fast carbs as unhealthier and more fattening than low-GI “slow carbs.” Despite popular perception of the superiority of low-GI diets for weight loss and obesity prevention, published research on the topic has produced conflicting interpretations of results (5–14).

See my post yesterday https://forum.diabetes.org.uk/board...besity-beyond-calories-in-calories-out.98436/ for the latest on the CIM and the competing "Energy Balance Model", by experts.
 
I did two experiments on myself to check. GI and GL are so not relevant for blood glucose management that I abandoned the concept as flawed in the extreme.
 
everydayupsanddowns said:
The data around GI seemed pretty unconvincing for BG management when the 2015 NICE T1 guidelines were in development too if memory serves too.

I’m not sure, but maybe the sampling and methodology just isn’t robust enough. Getting an average value from 100 people eating 50g in carbs of one single thing, just doesn’t fully reflect the complexity of mixed meals, and the individual variation of gut biome, metabolism, genetic components etc. Many folks on the forum have found that the common suggestion from DNs to switch to brown versions of carbs is unlikely to help all that much.

But at the same time, I don’t think it’s completely useless at an individual level either - because some of the indications (at least from a BG perspective) may be helpful if you haven’t got the opportunity to check your own individual response to things.

Where scientific studies have to isolate the action and confound for variables to see whether or not this one thing ‘works’, I think it can miss the interactions and ‘more than the sum of its parts’ effect that can happen when things combine (or compete)?
Click to expand...
There is just wild variability in glycemic responses. When you dig into the values listed by the GI gatekeepers like University of Sydney, they always seem to be based on a handful of responses with such a wide spread, that taking an average value as something meaningful just seems silly.

As this paper puts it:

Accurate assignment of GI values to foods from a diet record or FFQ is difficult (79). Factors that strongly affect a food's GI, such as variety and cooking/processing methods, are rarely specified in sufficient detail to ensure that the actual GI of the food eaten accurately reflects the assigned GI. For instance, the University of Sydney's GI database lists 27 values for brown rice ranging from 48 to 87 and 66 GI values for white rice ranging from 17 to 94 (80). Moreover, significant interindividual variability and intraindividual reproducibility in repeat GI testing under controlled conditions further complicate interpretation of GI data (81, 82). In a cohort of nearly 800 adults, the glycemic response to white bread varied by >5-fold when comparing the bottom 10% and top 10% of the individual postprandial glycemic responses (82). Finally, glycemic responses across individuals are highly heterogeneous and subject to variation due to age, genetics, physical activity, insulin sensitivity, and BMI (82).
 
I’ve never heard of GI being associated with weight loss only ever with bg control ( avoiding spikes) since the BDA ( aka DUk) ran a special edition of Balance all about GI in the mid 1990s. The BDA also funded that Australian woman’s research on GI. Of course GL came in since then.
 
Bruce Stephens said:
It was promoted for that. For example the rather old web site http://www.gidiet.com/ba/index.html

(I agree I don't remember any association with meaningful weight loss, but there were certainly diets promoted around the idea.)
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I certainly remember the Low GI diet, I probably had the book at once stage! I remember doing it to shift a bit of post-baby weight. The advantage was, that if you stuck to the list of Low GI foods, you automatically cut out a lot of cr*p like sweets, cakes, and biscuits, cheap factory made white bread, etc. So you probably ate less, but didn’t feel hungry. I also remember the F Plan diet. (probably before your time) I did that successfully to shift a stone for my wedding day. Again, you ate half a bowl of high fibre cereal twice a day, and that kept you feeling full and kept you off the cake! Sometimes diets aren’t about what you eat, but more about what you don't!
 
Whatever you think about the report, which has no relevance to diabetics, neither does it contain any reference to diabetes, the people who author this report own up to a few things...

"Author disclosures: GAG, JMJ, and SSA are members of the Scientific Advisory Board of the Grain Foods Foundation; GAG is a member of the Scientific Advisory Boards of the Wheat Foods Council and Ardent Mills, LLC; JMJ and SSA are members of the Scientific Advisory Council to the Quality Carbohydrate Coalition."
 
I lost over 2stone by following a low GI diet about 10 years ago but I put it back on when I stopped of course. 🙄 I agree with @Robin that it is what the low GI removes from your diet than what it contains.

For me low carb seems a more sustainable way to maintain a healthy body weight.
 
Robin said:
I certainly remember the Low GI diet, I probably had the book at once stage! I remember doing it to shift a bit of post-baby weight. The advantage was, that if you stuck to the list of Low GI foods, you automatically cut out a lot of cr*p like sweets, cakes, and biscuits, cheap factory made white bread, etc. So you probably ate less, but didn’t feel hungry. I also remember the F Plan diet. (probably before your time) I did that successfully to shift a stone for my wedding day. Again, you ate half a bowl of high fibre cereal twice a day, and that kept you feeling full and kept you off the cake! Sometimes diets aren’t about what you eat, but more about what you don't!
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Yes, I remember the F plan diet also the Mazel diet which advocated eating foods mainly fruits in a particular order, I tried that one and spent much time on the loo.
 
mikeyB said:
Whatever you think about the report, which has no relevance to diabetics, neither does it contain any reference to diabetes, the people who author this report own up to a few things...

"Author disclosures: GAG, JMJ, and SSA are members of the Scientific Advisory Board of the Grain Foods Foundation; GAG is a member of the Scientific Advisory Boards of the Wheat Foods Council and Ardent Mills, LLC; JMJ and SSA are members of the Scientific Advisory Council to the Quality Carbohydrate Coalition."
Click to expand...
Oops! That doesn't look so great.

And the study's methodlogy looks pretty rudimentary.
 
Started to incorporate low gi foods after giving low carb go for few months then returning to more normal diet, certainly helps with bg control but wasn't aware about any weight loss claims.
 
Eddy Edson said:

Metastudy published last November.

nmab093fig1.jpg


Sod-all difference, and sometimes higher GI associated with lower BMI.

In general:

In view of all the contrary evidence from observational cohort studies and meta-analyses of RCTs, it is surprising that the hypothesis that low-GI (“slow-carb”) diets are superior for weight loss and obesity prevention persists. Carbohydrate quality, including GI, clearly impacts many health outcomes (17, 18, 25), and several meta-analyses have reported higher risks of T2D, cardiovascular disease, and stroke associated with high-GI diets (25, 86–89). However, GI as a measure of carbohydrate quality appears to be unimportant as a determinant of BMI or diet-induced weight loss. We contend that GI is an imprecise measure of the glycemic response of a food when applied to foods in a meal, and that the GI assigned to foods from an FFQ may differ significantly from actual GI. Nutrient density, dietary fiber and whole-grain content of carbohydrates, and percentage of added sugar, are more important qualities (17, 18, 78). Further, a focus on staple carbohydrate foods and the positive nutrients they contribute to diet quality as compared with the detractor nutrients associated with indulgent foods is important in characterizing the quality of carbohydrates. As for body weight and obesity, there is scant scientific evidence that low-GI diets are superior to high-GI diets for weight loss and obesity prevention.
Click to expand...

Just in the context of PreDiabetes and Diabetes - how about ‘Glycemic Load’?
 
A at
Burylancs said:
I’ve never heard of GI being associated with weight loss only ever with bg control ( avoiding spikes) since the BDA ( aka DUk) ran a special edition of Balance all about GI in the mid 1990s. The BDA also funded that Australian woman’s research on GI. Of course GL came in since then.
Click to expand...

Quite.
 
I certainly remember her. Nutter. I was married before the 1980s started, so I do remember the 1980s. I became a GP in 1980.
 
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