Can Sugar Be Stored as Fat in the Body?
Yes, sugar is definitively converted to fat in the body through a process called hepatic de novo lipogenesis (DNL), which occurs when excess glucose or fructose exceeds what can be immediately oxidized for energy or stored as glycogen. 1
The Biochemical Mechanism
When glycogen stores are replete, excess glucose is converted to fat via hepatic de novo lipogenesis in the liver. 1 This is a well-established metabolic pathway that occurs under conditions of carbohydrate excess. 1
Glucose vs. Fructose Pathways
The conversion process differs slightly depending on the type of sugar consumed:
Glucose: High doses of rapidly digested glucose induce postprandial hyperglycemia and hyperinsulinemia. When glycogen stores are full, this excess glucose is further converted to fat via hepatic de novo lipogenesis. 1
Fructose: High doses of rapidly digested fructose have little influence on blood glucose or insulin levels, but more directly stimulate hepatic de novo lipogenesis, hepatic and visceral adiposity, and uric acid production. 1
Both glucose and fructose are harmful via distinct and partly overlapping pathways when consumed in high doses. 1
Clinical Consequences of Sugar-to-Fat Conversion
Excessive glucose intake causes increased lipogenesis and fat tissue deposition together with subsequent liver steatosis and enhanced production of VLDL triglycerides by the liver. 1 This has several important clinical implications:
Hepatic Effects
- Glucose modulates adipose tissue metabolism and mass both directly and indirectly by increasing insulin secretion and plasma concentration. Hyperinsulinemia is a key inducer of lipogenesis and adipose tissue expansion. 1
- High glucose contributes to non-alcoholic fatty liver disease (NAFLD) by enhancing circulating insulin, which in turn contributes to hepatic lipogenesis. 1
- High carbohydrate intake, both in hypercaloric as well as eucaloric conditions, leads to lipogenesis. 1
Metabolic Complications
- The conversion of glucose into lipids partially accounts for the increase in energy expenditure observed with high rates of glucose infusion. 1
- Studies in healthy adults show that high carbohydrate feeding leads to an increase in total VLDL triglyceride secretion rate from de novo synthesis, primarily due to stimulation of the secretion of preformed fatty acids. 1
- Hepatic steatosis results when export of VLDL triglycerides does not keep pace with triglyceride production. 1
Important Clinical Context
Dose and Form Matter
Low doses of slowly digested glucose or fructose (e.g., as found in fruit) have minimal cardiometabolic harms, while high doses of rapidly digested sugars are harmful. 1 The key distinction is:
- Rapidly digested, refined sugars (white bread, white rice, added sugars, sugar-sweetened beverages) promote harmful metabolic effects. 1
- Slowly digested carbohydrates in whole foods (fruits, legumes, vegetables, minimally processed whole grains) are protective. 1
Evidence from Intervention Studies
Removal of sugar from diets of children with obesity for only 9 days consistently reduced de novo lipogenesis and liver fat and improved glucose and lipid metabolism. 2 This demonstrates the rapid reversibility of sugar-induced fat accumulation when dietary sugar is restricted.
Clinical Recommendations
Major health organizations now make evidence-based recommendations to limit consumption of simple sugars to no more than 5% to 10% of daily intake. 2 The 2015 Dietary Guidelines Advisory Committee explicitly advises restriction of both refined grains and added sugars. 1
Common Pitfall to Avoid
Do not focus solely on added sugars while ignoring refined complex carbohydrates. Targeting added sugars alone could push consumers toward foods low in added sugars but rich in equally harmful refined complex carbohydrates (e.g., many breakfast cereals, breads, crackers). 1