13th February 2019, Dr Chee L Khoo
It’s all too confusing. It used to be low fat diet. It’s now low carbohydrate (carb) diet. Some studies show that low carb diet loses more weight than low fat diet while others show the opposite. Yet, other studies show no significant difference between the diets. So, which is it then? Have you wondered that perhaps, we are looking at different patients responding to different diets. Perhaps, for certain patients a low carb diet loses more weight while for others, low fat diet may trump the low carb diet.
Perhaps, if there are biochemical markers that we could use that can help predict who may benefit from which diet. Indeed, several studies containing small number of subjects looked at whether fasting plasma insulin (FI) concentration or indices of insulin secretion predict the weight loss response to low-carbohydrate and low-fat (with high glycaemic load) diets, but results have been equivocal [2–6]. A recent retrospective analysis of previously published trial data sought to investigate whether fasting plasma glucose (FPG) and fasting insulin may predict response to either low carbohydrate or low fat diet.
In the original trial lasting 24 months, 307 participants were randomised to either low carbohydrate diet (<20g total daily carbohydrates) or low fat diet (containing 55, 30, 15% of carbohydrate, fat and protein). Total energy intake was 1200-1500 kcal/day for women and 1500-1800 kcal/day for men. Baseline body weight, fasting plasma glucose and insulin were measured after 12 hour overnight fasting. Insulin sensitivity (SI) were assessed using intravenous glucose tolerance test. Patients were reviewed at 3,6, 9, 12 and 24 months.
What did they find?
The drop out rate was higher in the low carb group compared with the low fat group (44% vs 32% p= 0.031). This is particular so in participants with high FPG and high FI (47% vs 10% p=0.018). Although overall, there were no difference in weight loss between the two diets, when they broke down the data according to whether the participants were normoglycaemic or prediabetic (fasting glucose between 5.6-6.9 mmol/L) and whether they had low FI (<76 pmol/L) or high FI (>76 pmol/L), there were differences between groups.
Results
Normoglycaemic participants
Overall average weight loss 6-8kg but it didn’t matter whether it was low fat or low carb diets. Both groups lost weight. There were no significant difference with either diet whether the FI was taken into consideration.
Pre-diabetic participants
Prediabetics who had high FI lost more weight with low fat diets than low carb diet (-0.5 kg vs -7.6 kg). Prediabetics who had low FI lost more weight with low carb diet than low fat diet (-15.8kg vs -9.6kg).
If we also use insulin sensitivity, participants with high FI and low SI lost more weight on low fat diet than low carb diet (-7.1kg vs -2.0kg). There were no difference between the diet groups with other combinations of FI and SI.
In summary, in this study, patients with prediabetes AND high FI lose more weight with low fat diet while participants with prediabetes AND low FI lose more weight with low carb diet. While some studies concur with the findings in this study (4), other studies have the opposite results: participants with high FI lost more weight on low carb diet while participants with low FI lost more weight with low fat diet (1-7).
Perhaps, separation into groups based on fasting glucose and fasting insulin may need some more refining. Fasting plasma glucose may not be sufficient to exclude patients who has diabetes already and hence, have limited insulin secretion. Low insulin may not reflect the level of insulin resistance. We will need more data and more studies.
Access the abstract here.
- Cornier M, Donahoo WT, Pereira R, Gurevich I, Westergren R, Enerback S, et al. Insulin sensitivity determines the effectiveness of dietary macronutrient composition on weight loss in obese women. Obes Res. 2005;13:703–
- McClain AD, Otten JJ, Hekler EB, Gardner CD. Adherence to a low‐fat vs. low‐carbohydrate diet differs by insulin resistance status. Diabetes, Obes Metab. 2013;15:87–
- Hjorth MF, Ritz C, Blaak EE, Saris WH, Langin D, Poulsen SK, et al. Pretreatment fasting plasma glucose and insulin modify dietary weight loss success: results from 3 randomized clinical trials. Am J Clin Nutr. 2017;106:499–
- Hjorth MF, Due A, Larsen TM, Astrup A. Pre-treatment fasting plasma glucose modifies dietary weight loss maintenance success: results from a stratified RCT. Obesity. 2017;25:2045–
- Ballesteros-Pomar MD, Calleja-Fernandez AR, Vidal-Casariego A, Urioste-Fondo AM, Cano-Rodríguez I. Effectiveness of energy-restricted diets with different protein: carbohydrate ratios: the relationship to insulin sensitivity. Public Health Nutr. 2010;13:2119–
- Shyam S, Arshad F, Ghani RA, Wahab NA, Safii NS, Nisak MYB, et al. Low glycaemic index diets improve glucose tolerance and body weight in women with previous history of gestational diabetes: a six months randomized trial. Nutr J. 2013;12:68.
- Ghani RA, Shyam S, Arshad F, Wahab NA, Chinna K, Safii NS, et al. The influence of fasting insulin level in post-gestational diabetes mellitus women receiving low-glycaemic-index diets. Nutr Diabetes. 2014;4:e107.
- Mads F. Hjorth, Arne Astrup, Yishai Zohar, et al. Personalized nutrition: pretreatment glucose metabolism determines individual long-term weight loss responsiveness in individuals with obesity on low-carbohydrate versus low-fat diet. International Journal of Obesity 19th Dec 2019, https://doi.org/10.1038/s41366-018-0298-4