Gluten-free diet intervention reduces thiamine intake in two weeks, increases glycaemic response and decreases body weight in four weeks, with no long term nutritional deficiencies

Figures & data

Table 1. A list of foods given to the participants to choose gluten-free products in study two. (Source: Coeliac UK; www.coeliac.org.uk).

	Gluten free	Check to confirm	Not gluten free
Grains and alternatives	Amaranth, buckwheat, chestnut, corn (maize), millet, polenta (cornmeal), quinoa, rice, sago, sorghum, soya, tapioca, teff		Barley, bulgar wheat, couscous, dinkel, durum wheat, einkorn, emmer wheat, Farro, Khorasan wheat (commercially known as Kamut), rye, semolina, spelt, triticale, wheat
Flours	All flours that are labelled gluten free		Flours made from wheat, rye or barley, e.g. plain flour, self-rising flour, etc.
Oats	Oats, oatcakes		Porridge oats, oat milk, oat-based snacks that are not labelled gluten free
Breads, cakes and biscuits	All products labelled gluten free including biscuits, breads, cakes, crackers, muffins, pizza bases, rolls, scones	Macaroons, meringues	All biscuits, breads, cakes, chapattis, crackers, muffins, pastries and pizza bases made from wheat, rye or barley flour
Breakfast cereals	All products labelled gluten free including millet porridge, muesli, rice porridge, corn and rice-based cereals	Buckwheat, corn, millet and rice-based breakfast cereals and those that contain barley malt extract	Muesli, wheat-based breakfast cereals
Pasta and noodles	All products labelled gluten free including corn (maize) pasta, quinoa pasta, rice pasta	Rice noodles, buckwheat noodles	Canned, dried and fresh wheat noodles and pasta
Meat and poultry	All fresh meats and poultry, cured pure meats, plain cooked meats, smoked meats	Any meat or poultry marinated or in a sauce, burgers, meat pastes, patés, sausages	Meat and poultry cooked in batter or breadcrumbs, breaded ham, faggots, haggis, rissoles
Meatless alternatives	Plain tofu	Marinated tofu, soya mince, falafel, vegetable and bean burgers
Fish and shellfish	All dried, fresh, kippered and smoked fish, shellfish, fish canned in brine, oil and water	Fish pastes, fish patés, fish in sauce	Fish or shellfish in batter or breadcrumbs, fish cakes, fish fingers, taramasalata
Cheese and eggs	All cheese and eggs		Scotch eggs
Milk and milk products	All milk (liquid and dried), all cream (single, double, whipping, clotted, soured and crème fraiche), buttermilk, plain fromage frais, plain yoghurt	Coffee and tea whiteners, fruit and flavoured yoghurt or fromage frais, soya desserts, rice milk, soya milk, nut milks	Yoghurt with muesli or wholegrains

Table 2. Characteristics of participants who followed Gluten-containing diet (n = 11) and Gluten-free diet (n = 11) in study one.

	Diet type	Mean ± SD	p Value	95% CI		z
				LL	UL
Age (years)	GC	30 ± 9.0	.791			−1.87
	GF	29 ± 9.0
Weight (kg)	GC	73.1 ± 14.7	.115	−2.55	21.72	–
	GF	63.5 ± 12.5
BMI^a (kg/m^2)	GC	23.4 ± 2.8	.711	−2.32	3.33	–
	GF	22.8 ± 3.5
Waist circumference (cm)	GC	76.5 ± 8.5	.122			−1.54
	GF	72.3 ± 7.7
Body fat (%)	GC	23.4 ± 9.0	.274	−9.94	3.04	–
	GF	26.9 ± 4.5
Systolic blood pressure (mmHg)	GC	114.4 ± 6.6	.413	−4.56	10.63	–
	GF	111.4 ± 9.6
Diastolic blood pressure (mmHg)	GC	73.6 ± 7.2	.616	−9.0	5.47	–
	GF	75.4 ± 8.5
Baseline glucose (mmol/L)	GC	4.8 ± 0.5	.250	−0.24	0.64	–
	GF	4.6 ± 0.5
Baseline Insulin (mU/L)	GC	3.6 ± 3.0	.551	–	–	−0.60
	GF	3.2 ± 2.7

^aBMI was calculated as weight/height².

CI: confidence interval; LL: lower limit; UL: upper limit; z: standardised score; BMI: body mass index

Table 3. Participant characteristics (n = 11) before and after the Gluten-free diet intervention in study two.

	Diet phase	Mean ± SD	p Value	95% CI		Effect size
				LL	UL
Weight (kg)	Pre GFD	72.6 ± 16.6	.007	0.50	2.40	0.09
	Post GFD	71.2 ± 16.6
BMI^a (kg/m²)	Pre GFD	24.2 ± 3.5	.004	0.20	0.78	0.14
	Post GFD	23.7 ± 3.6
Waist circumference (cm)	Pre GFD	76.2 ± 10.6	.072
	Post GFD	75 ± 10.9
Body fat (%)	Pre GFD	25.3 ± 7.7	.127	−0.44	3.02
	Post GFD	24.0 ± 8.1
Systolic blood pressure (mmHg)	Pre GFD	113.7 ± 14.4	.423	−5.43	11.83
	Post GFD	110.5 ± 8.9
Diastolic blood pressure (mmHg)	Pre GFD	73.5 ± 9.9	.682	−6.08	8.88
	Post GFD	72.1 ± 9.9
Baseline glucose (mmol/L)	Pre GFD	4.6 ± 0.5	.595	−0.25	0.41
	Post GFD	4.5 ± 0.5
Baseline insulin (mU/L)	Pre GFD	3.7 ± 4.0	.551	−2.55	1.45
	Post GFD	4.3 ± 2.8

^aBMI was calculated as weight/height².

CI: confidence interval; LL: lower limit; UL: upper limit; BMI: body mass index

Figure 1. Change in (a) blood glucose concentration (mean ± SEM) and (b) plasma insulin concentration (mean ± SEM) in the GFD and GCD group during OGTT. GFD: Gluten free diet; GCD: Gluten-containing diet; OGTT; oral glucose tolerance test.

Figure 2. Change in (a) blood glucose concentration (mean ± SEM) and (b) plasma insulin concentration (mean ± SEM) during OGTT before and after the 4-week GFD intervention. Asterisk (*) denotes a significant difference (p<.05). OGTT: oral glucose tolerance test; GFD: Gluten free diet.

Table 4. The average daily energy and nutrient intake for participants in the gluten-containing diet group and gluten-free diet group (study one).

Nutrient	Diet type	Mean ± SD	p Value	95% CI		z
				LL	UL
Energy (kcal)	GC	2097.6 ± 909.4	.06	−33.93	1233.20	–
	GF	1497.9 ± 339.1	–	–	–	–
Fat (g)	GC	75.5 ± 35.1	.49	–	–	−0.69
	GF	60.7 ± 13.8	–	–	–
Protein (g)	GC	95.9 ± 47.2	.10	–	–	−1.65
	GF	67.7 ± 17.9	–	–	–	–
Carbohydrate (g)	GC	223.4 ± 85.0	.07	−4.86	120.46	–
	GF	165.6 ± 51.9	–			–
Fibre (g)	GC	26.1 ± 10.2	.61	−6.86	11.44	–
	GF	23.9 ± 10.3	–			–
Free Sugar (g)	GC	16.8 ± 10.0	.21	−3.14	13.34	–
	GF	11.7 ± 8.5	–	–	–	–
Iron (mg)	GC	10.9 ± 5.0	.14	−1.03	6.89	–
	GF	8.0 ± 3.8	–	–	–	–
Folate (ug)	GC	267.8 ± 137.4	.07	−4.79	185.70	–
	GF	177.4 ± 63.7	–	–	–	–
Thiamine (mg)	GC	1.7 ± 1.3	.07	–	–	−1.81
	GF	1.0 ± 0.4	–	–	–	–

CI: confidence interval; LL: lower limit; UL: upper limit

Table 5. Nutritional intake before and after the 4-week Gluten-free diet intervention (study two).

	Diet phase	Mean ± SD	p Value	95% CI		Effect size	Z
				LL	UL
Energy (kcal)	Pre GFD	1877.0 ± 945.8	.286	–	–	–	−1.07
	Post GFD	1681.0 ± 670.5		–	–	–
Fat (g)	Pre GFD	70.1 ± 35.9	.350	–	–	–	−0.94
	Post GFD	64.2 ± 65.6	–	–	–	–
Protein (g)	Pre GFD	106.3 ± 66.8	.091	–	–	–	−1.69
	Post GFD	94.3 ± 65.6		–	–	–
Carbohydrate (g)	Pre GFD	197.0 ± 97.5	.374	–	–	–	−0.89
	Post GFD	174.6 ± 68.9	–	–	–	–	–
Fibre	Pre GFD	24.8 ± 10.4	.378	−3.02	7.29	–	–
	Post GFD	22.7 ± 8.8	–	–	–	–	–
Free sugars (g)	Pre GFD	13.4 ± 11.1	.857	−7.09	8.37		–
	Post GFD	12.7 ± 11.2	–	–	–	–	–
Sodium (mg)	Pre GFD	1834.0 ± 885.7	.091	–	–	–	−1.69
	Post GFD	1348.0 ± 606.8	–	–	–	–	–
Calcium (mg)	Pre GFD	719.6 ± 400.9	.276	−114.43	360.06	–	–
	Post GFD	596.7 ± 244.8	–	–	–	–	–
Iron (mg)	Pre GFD	10.7 ± 4.9	.326	−1.37	3.73	–	–
	Post GFD	9.5 ± 5.1	–	–	–	–	–
Thiamine (mg)	Pre GFD	1.7 ± 1.2	.021^*	–	–	0.54	−2.31
	Post GFD	1.2 ± 0.6		–	–	–	–
Niacin (mg)	Pre GFD	44.2 ± 34.0	.424	–	–	–	−0.80
	Post GFD	42 ± 36.8	–	–	–	–	–

CI: confidence interval; LL: lower limit; UL: upper limit^*Statistically significant difference - p < .05.

Data availability statement

Data available on request from the authors. The data that support the findings of this study are available from the corresponding author [PST], upon reasonable request.