A low carb, low fat diet is an eating pattern that restricts both carbohydrates and dietary fat at the same time, leaving protein as the dominant source of calories. In practice, this means most of your plate is filled with lean protein sources and non-starchy vegetables, while bread, pasta, rice, oils, butter, and fatty cuts of meat are all minimized. It’s a narrower approach than either a standard low-carb or low-fat diet on its own, and it comes with both potential benefits and real nutritional tradeoffs worth understanding.
How the Macronutrient Split Works
A typical balanced diet draws 45 to 65% of calories from carbohydrates, 20 to 35% from fat, and 10 to 35% from protein. A low carb, low fat diet flips that balance dramatically. While there’s no single official definition, weight-loss versions of this approach often target roughly 10 to 30% of calories from carbs, 30 to 40% from fat, and 40 to 50% from protein. The most aggressive clinical version, called a protein-sparing modified fast, pushes even further: fewer than 20 grams of carbohydrates per day, virtually no added fats, and protein intake calculated at about 1.2 to 1.5 grams per kilogram of body weight. That extreme version typically provides around 800 calories a day and requires medical supervision.
The key distinction from other popular diets is that you’re cutting two of the three macronutrients at once. A ketogenic diet cuts carbs but encourages high fat intake. A traditional low-fat diet cuts fat but allows plenty of grains and starches. This hybrid approach restricts both, which significantly limits what you can eat and makes protein the caloric backbone of every meal.
What You Can Actually Eat
The food list for a low carb, low fat diet is relatively short. Lean proteins are the foundation: chicken breast, turkey, white fish, shrimp, egg whites, and tofu. Fatty fish like salmon is a borderline choice since it contains healthy fats but more total fat than white fish. Non-starchy vegetables round out most meals: broccoli, kale, spinach, cucumbers, bell peppers, cauliflower, and lettuce. Greek yogurt (nonfat or low-fat) and cottage cheese fit the profile as well.
What gets eliminated is a long list. On the carb side, you’re avoiding bread, pasta, rice, potatoes, most fruits, cereals, and anything with added sugar. On the fat side, you’re cutting out oils, butter, nuts, seeds, avocado, cheese (except low-fat versions), and fatty meats like bacon or ribeye. That double restriction is what makes this approach feel notably limited compared to diets that only cut one macronutrient.
Cooking without added oil is a practical skill you’ll need. Sautéing vegetables in a dry pan or with a small amount of water or broth works well, starting with high-water-content vegetables first. Air fryers and convection ovens crisp food without oil by circulating hot air around it. Baking on silicone mats eliminates the need to grease pans. These techniques take some adjustment but become routine quickly.
Why People Try This Approach
The logic behind cutting both carbs and fat is straightforward: carbohydrates drive insulin spikes that can increase hunger, while fat is the most calorie-dense macronutrient at 9 calories per gram (compared to 4 for protein and carbs). By reducing both, you’re theoretically controlling appetite and cutting calories simultaneously. Protein also has the highest thermic effect of any macronutrient, meaning your body burns more energy digesting it, and it’s the most satiating, keeping you fuller longer.
NIH research comparing low-fat and low-carb diets found that each approach had distinct metabolic effects. A low-carb diet produced lower and more stable blood sugar and insulin levels throughout the day. A low-fat, plant-based diet curbed appetite more effectively. Only the low-fat diet led to significant body fat loss in the short term, while both produced weight loss overall. A combined approach aims to capture both sets of benefits, though it hasn’t been studied as extensively as either diet alone.
How It Compares to Other Diets
A meta-analysis of 13 randomized controlled trials involving over 1,400 patients found that very-low-carbohydrate ketogenic diets (under 50 grams of carbs per day) produced about 0.9 kilograms more weight loss long-term than low-fat diets. The ketogenic dieters also saw improvements in triglycerides, “good” HDL cholesterol, and diastolic blood pressure. However, their LDL (“bad”) cholesterol also increased, a tradeoff that doesn’t occur on low-fat diets. There were no significant differences between the two approaches for fasting blood sugar, insulin levels, or markers of inflammation.
A low carb, low fat diet sidesteps the LDL increase that comes with high-fat keto eating, since you’re not loading up on saturated fat. But it also misses out on the steady ketosis that drives some of the ketogenic diet’s metabolic effects. It occupies a middle ground that may appeal to people concerned about heart health markers but still wanting lower insulin and blood sugar responses.
Nutritional Risks of Dual Restriction
Cutting two macronutrient groups simultaneously creates real gaps in your nutrient intake. Research on low-carbohydrate eating patterns found consistent shortfalls in fiber, magnesium, potassium, and vitamins A, D, and E. Men were additionally low in vitamin C, and women over 31 were low in folate. When you also restrict fat, you compound the problem: your body needs dietary fat to absorb fat-soluble vitamins (A, D, E, and K). Below about 10% of total calories from fat, absorption of these vitamins becomes unreliable. Vitamin E deficiency, for example, has been linked to nerve damage and anemia.
The minimum fat intake for adults is estimated at 10 to 15% of total calories just to meet basic energy needs, with an additional 3 to 5% needed specifically for essential fatty acids like linoleic acid and linolenic acid. Your body cannot manufacture these fats on its own. Dropping below these thresholds can affect hormone production, cell membrane integrity, and brain function. For most people, keeping fat intake above 15 to 20% of calories is a reasonable floor even on a restricted diet.
Effects on Thyroid Function
Very low carbohydrate intake can shift thyroid hormone levels. A crossover trial comparing a ketogenic diet to a high-carb, low-fat diet in healthy adults found that the ketogenic phase significantly lowered active thyroid hormone (T3) while increasing inactive T4. The high-carb phase did not change T3 levels. Thyroid-stimulating hormone stayed the same on both diets, meaning the thyroid gland itself wasn’t malfunctioning. Instead, the body appeared to slow its conversion of inactive thyroid hormone into the active form, possibly as an energy-conservation response. Since active thyroid hormone directly influences your metabolic rate, this shift could make weight loss harder over time on very low carb intakes.
Sticking With It Long Term
Adherence is the biggest practical challenge with any restrictive diet, and dual restriction makes it harder. A 12-month randomized trial of 148 people assigned to either low-carb or low-fat diets found that about 20% of participants in each group dropped out before the year was up. Counseling session attendance averaged only about 53 to 57%. Composite adherence scores were similar between groups and only modestly above the midpoint, suggesting that even restricting one macronutrient is difficult to sustain. Restricting both simultaneously leaves fewer food options and less flexibility in social situations, which likely makes long-term compliance even more challenging.
The protein-sparing modified fast, the most extreme version of this approach, addresses the adherence problem by design: it’s meant to be temporary. The intensive phase lasts weeks to a few months, followed by a structured refeeding phase where carbohydrates are gradually reintroduced (up to 45 grams in month one, 90 grams in month two) and protein portions are slowly reduced. This phased approach acknowledges that severely restricting both carbs and fat is not something most people can or should do indefinitely.
Making It Work Practically
If you want to try a moderate version of this approach without going to clinical extremes, the goal is to center meals around lean protein with generous portions of non-starchy vegetables, while keeping small amounts of healthy fat in the mix for nutrient absorption. A breakfast might be an egg-white omelet with spinach and bell peppers. Lunch could be grilled chicken breast over a large kale salad with a light vinaigrette. Dinner might be baked white fish with steamed broccoli and cauliflower rice.
A daily multivitamin is worth considering given the nutrient gaps this eating pattern creates. Paying particular attention to magnesium, potassium, and fiber intake through vegetables and possibly supplementation can help offset the most common deficiencies. Keeping fat intake at a minimum of 15 to 20% of calories, rather than trying to eliminate it entirely, protects both your hormone balance and your ability to absorb the vitamins in the vegetables you’re eating.